Hitachi Simple Modular Storage Copy-onWrite SnapShot User’s Guide FASTFIND LINKS Document Organization Product Version Getting Help Table of Contents i # MK-97DF8018-00
© 2007 Hitachi Data Systems Corporation, ALL RIGHTS RESERVED Notice: No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying and recording, or stored in a database or retrieval system for any purpose without the express written permission of Hitachi Data Systems Corporation (hereinafter referred to as “Hitachi Data Systems”).
Preface This document provides instructions on assessing your snapshot requirements, designing an implementation to meet those requirements, and implementing and operating Copy-on-Write Snapshot software using the Storage Navigator 2 graphical user interface.
Document Revision Level This section provides a history of the revision changes to this document. • Revision MK-97DF8018-00 Date October 2007 Description Initial Release Safety and Warnings This document uses the following symbols to draw attention to important safety and operational information. The Danger, Electric Shock, and ESD symbols are included only in hardware manuals.
Document Organization The following table provides an overview of the contents and organization of this document. Click the chapter title in the first column to go to that chapter. The first page of every chapter or appendix contains a brief list of the contents of that section of the manual, with links to the pages where the information is located. • Chapter/Appendix Title Description Chapter 1, SnapShot Provides descriptions of SnapShot components and how they work together.
Document Conventions The following table describes the typographic conventions used in this document. • Convention Description Bold Indicates text on a window, other than the window title, including menus, menu options, buttons, fields, and labels. Example: Click OK. Italic Indicates a variable, which is a placeholder for actual text provided by the user or system. Example: copy source-file target-file. Note: Angled brackets (< >) are also used to indicate variables.
Getting Help If you have questions after reading this guide, contact an Hitachi Data Systems authorized service provider[H1] or visit the Hitachi Data Systems support website, http://support.hds.com. Support Contact Information If you purchased this product from an authorized Hitachi Data Systems reseller, contact that reseller for support. For the name of your nearest Hitachi Data Systems authorized reseller, refer to the Hitachi Data Systems support web site for locations and contact information.
viii Preface Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
Table of Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii Document Revision Level . . . . . . . . . . . . . . Safety and Warnings . . . . . . . . . . . . . . . . . Intended Audience . . . . . . . . . . . . . . . . . . Product Version. . . . . . . . . . . . . . . . . . . . . Release Notes . . . . . . . . . . . . . . . . . . . . . . Document Organization . . . . . . . . . . . . . . . Referenced Documents . . . . . . . . . . . . . . .
Lifespan Based on Backup Requirements . . . . . . . . . . Lifespan Based on Business Uses . . . . . . . . . . . . . . . Establishing the Number of V-VOLs that Are Required. . . Establishing Data Pool Size. . . . . . . . . . . . . . . . . . . . . . . . . Measuring Workload Data . . . . . . . . . . . . . . . . . . . . . . Rule of Thumb Calculation . . . . . . . . . . . . . . . . . . . . Calculating Maximum Capacity . . . . . . . . . . . . . . . . . . . . . . Operating System Considerations . . . . . . . . . .
7 Monitoring and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 Monitoring SnapShot . . . . . . . . . . . . Monitoring Pair Status . . . . . . . . Monitoring Data Pool Usage . . . . Expanding the Data Pool . . . . . . . . . Other Methods for Lowering Data 8 ........ ........ ........ ........ Pool Load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xii Contents Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
1 SnapShot Overview Snapshot creates virtual copies of data volumes within Hitachi Simple Modular Storage systems. These copies can be used for recovery from logical errors. They are identical to the original volume at the point in time they were taken. This guide provides instructions for planning and designing, configuring and testing, and using and monitoring SnapShot.
Copy-on-Write SnapShot Software Hitachi’s Copy-on-Write Snapshot software creates virtual backup copies of any data volume within the Simple Modular Storage systems with minimal impact to host service or performance levels. These snapshots are suitable for immediate use in decision support, software testing and development, data backup, or rapid recovery operations.
• Figure 1-1: SnapShot functional components The following sections describe how these components work together. How SnapShot Works SnapShot creates a virtual duplicate volume of another volume. This volume “pair” is created when you: • Select a volume that you want to replicate • Identify another volume that will contain the copy • Associate the primary and secondary volumes • Create a snapshot of the primary volume data in the virtual (secondary) volume.
Volume Pairs—P-VOLs and V-VOLs A volume pair is a relationship established by SnapShot between two volumes. A pair consists of a production volume, which contains the original data and is called the primary volume (P-VOL), and from 1 to 32 virtual volumes (V-VOLs), which contain copies of the P-VOL. The P-VOL and its VVOL(s) are located in the same Simple Modular Storage system. A V-VOL is a mirror image of the P-VOL at the time of the snapshot.
• Figure 1-2: V-VOL Maintains SnapShot Data SnapShot Overview Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide 1–5
Data Pools After a snapshot, the V-VOL maintains a static copy of the P-VOL even as new writes are updating the P-VOL. To do this, before an updated block is written to the P-VOL, SnapShot sends the data that is being replaced to the data pool. Pointers in the V-VOL are updated to locate the replaced data that is now located in the data pool, thus maintaining the V-VOL point-in-time image of the P-VOL. The data pool’s function in the SnapShot process is illustrated in Figure 1-2.
2 Planning and Design A backup insures that a volume with bad or missing data can be restored. With SnapShot you create copies of your production data that can be used for backup and other uses. Creating a backup system that fully supports business continuity is best done when SnapShot is configured to match your business needs. This chapter guides you in planning a configuration that meets organization needs and the workload requirements of your host application.
The Plan and Design Workflow The SnapShot planning effort consists of finding the number of V-VOLs your organization requires for the P-VOL, the V-VOL(s)’ lifespan — how long they must be held before being updated again — the frequency that snapshots are taken, and the size of the data pool. The answers are determined by analyzing the organization’s business needs and measuring the write workload that is generated by the host application.
Ideally, a business desires no data loss. In the real world, disasters occur and data is lost. You or your organization’s decision makers must decide the number of business transactions, the number of hours required to key in lost data, and so on. • If losing 4 hours of business transaction is acceptable, but not more, backups should be planned every 4 hours. If 24 hours of business transaction can be lost, backups may be planned every 24 hours.
• If the snapshot is to be used as a disk-based backup available for online recovery, you can determine the lifespan by multiplying the number of generations of backup you want to keep online by the snapshot frequency. For example: Generations held = 4 Snapshot frequency = 4 hours 4 x 4 = 16 hours V-VOL lifespan = 16 hours Lifespan Based on Business Uses • If you use snapshot data (the V-VOL) for testing an application, the testing requirements determine the amount of time a snapshot is held.
Establishing Data Pool Size The data pool holds data from the P-VOL that is being replaced. By holding this original data in the data pool, the mirror image of the V-VOL is maintained at the time of the snapshot. You determine the size of the data pool that your system requires by: • Measuring the amount of write workload that passes from the host application to the P-VOL. Write workload is the megabytes per second that are written to the primary volume over a specific time.
2. At the end of the period, convert the data to MB/second, if it is not already so, and import into a spreadsheet tool. Figure 2-3 shows collected raw data, in megabytes per second in 10 minute segments. • Figure 2-3: Raw Data Example in MB/sec 3. Using the copy frequency established earlier, calculate averages over the collection period. Most spreadsheet tools have an average function.
b. Press Enter. This instructs the tool to calculate the average value in cells B2 through B7 and populates C4 with that data. c. Copy the value in C4. d. Highlight cells C5 to the last C cell in the last row of workload data in the spreadsheet. e. Right-click the highlighted cells and select the paste option. Excel maintains the logic and increments the formula values initially entered in C4. It then calculates all the point in time averages and populates the C cells.
5. Calculate the base data pool size for your primary/virtual volumes by multiplying the MB size of one V-VOL in Step 4 by the number of V-VOLs, which was established earlier. For example: 90,000 MB x 4 V-VOLS = 360,000 MB This is the base data pool size for a SnapShot system in which the copy frequency is 1 hour, the copy lifespan is 4 hours, and the number of copies (V-VOLs) is 4. 6. It is highly recommended that a safety factor of 20%, be calculated.
3. Multiply the base data pool size by the number of V-VOLs. Thus: 4 V-VOLs x 625 GB = 2500 GB (2.5 TB). Data Pool Key Points • The data pool must be on same controller as the P-VOL and V-VOL(s). • Data pool capacity should be at least 20 GB. • Up to 64 volumes can be assigned to a data pool. • When a volume is assigned to a data pool, it is no longer recognized by a host. Calculating Maximum Capacity Simple Modular Storage manages capacity for in-system replication systems in segments of 15.
Total PVOL size = 173.25 GB Total data pool size = 163.2 GB Thus: 173.25 GB / 5 = 34.65 GB 34.65 GB + 163.2 GB = 197.85 GB In this example, the SnapShot maximum capacity is 197.85 GB, well below the maximum supported capacity of 800 GB. If ShadowImage is used in addition to SnapShot 6. List the total size of SnapShot P-VOLs. Using the example above: Total SnapShot P-VOL capacity = 150 GB 7. List the total size of ShadowImage S-VOLs. For example: Total SI S-VOL = 14 TB (14,000 GB) 8.
b. Right-click the disk whose HLUN you want to know, then select Properties. The number displayed to the right of “LUN” in the dialog window is the HLUN. 2. Identify HLUN-to-LUN Mapping. a. In Start Storage Navigator Modular 2, select the desired array. b. In the array tree that displays, click the Group icon then click iSCSI Target icon in the Groups tree. c. On the iSCSI Target screen, select an iSCSI target. d. On the target screen, select the Logical Units tab. Find the identified HLUN.
Linux and LVM Configuration A host cannot recognize both a P-VOL and its V-VOL at the same time. Map the P-VOL and V-VOL to separate hosts. Windows Server 2003/Windows 2000 and Dynamic Disk Observe the following when using Windows Server 2003 dynamic disk: • You cannot make a P-VOL and a V-VOL into a dynamic disk; however you can use a P-VOL and a V-VOL as a dynamic disk. • When using a V-VOL with a secondary host, insure that the pair status is Split.
If any one of the dynamic disks is left unhidden, a Missing drive occurs. When this occurs, delete it manually using the diskpart delete command (CCI required).
• Copy dynamic disk volumes that consist of two or more LUs only after hiding all LUs from a host. When the copy is completed, you can have them recognized by a host. • 2–14 • A dynamic disk cannot be used with a cluster (MSCS, VCS, etc.). • A dynamic disk cannot be used with VxVM and HDLM.
3 Requirements This chapter describes minimum operational requirements.
System Requirements Table 3-1 shows the minimum requirements for SnapShot. See Appendix B, SnapShot Specifications for additional information. Table 3-1: Storage System Requirements Minimum Requirements • Simple Modular Storage system microcode: Version 1810/A or greater. • Storage Navigator Modular 2: Version 1.00 or greater. • CCI: Version 01-20-03/05 or greater—optional. CCI is provided for advanced users. • Number of controllers: 2.
4 Enabling and Disabling SnapShot SnapShot is bundled with the Simple Modular Storage system. It must be enabled before using. SnapShot can also be disabled.
Enabling/Disabling SnapShot To enable/disable SnapShot 1. In the Navigator 2 GUI, select the array where you want to enable SnapShot and click the Show & Configure Array button. 2. In the tree view, click Settings, then click Licenses. 3. Select SnapShot in the Licenses list, then click the Change Status button at the bottom of the page. The Change License screen appears. • 4. To enable, click the Enable: Yes check box. To disable, clear the Enable: Yes check box.
• 7. When ready, click the Yes, I have read ... check box at the bottom of the message, then click Reboot Array. The reboot time displays. If the Storage system does not respond after 15 minutes, check its condition. • 8. When rebooting has finished, a message appears stating that the restart is successful. Click Close.
4–4 Enabling and Disabling SnapShot Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
5 Configuring SnapShot This chapter describes the steps for setting up SnapShot.
Configuration Workflow The following configuration tasks must be completed for SnapShot functions to become operational. The P-VOL should be set up in your Simple Modular Storage system prior to SnapShot configuration. See Appendix B, SnapShot Specifications for more information. • Assign volumes for: • Data pools • Virtual volumes (V-VOL) Assign Volumes for the Data Pool The data pool stores differential data after the snapshot is created.
Set Up the Virtual Volume (V-VOL) (manual method) When the Backup Wizard in the Navigator 2 GUI is used, V-VOLs are created and set up automatically. You do not need to perform any V-VOL setup. If you are not using the Backup Wizard but the Create Pair procedure, then proceed with the instructions below. Using the Create Pair procedure is a more involved method that allows you to set copy pace, assign the pair to a group (and create a group), and automatically split the pair after creating.
5–4 Configuring SnapShot Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
6 Using SnapShot This chapter describes the SnapShot data replication workflow and processes. Details are provided for in-system replication along with sample scenarios using SnapShot functionality. SnapShot Replication Workflow Back Up Your Volume—Create a Pair Update the V-VOL Restore the P-VOL from the V-VOL Use the V-VOL for Tape Backup, Testing, Reports, Etc. Edit Pairs, Data Pool Delete Pairs, V-VOLs, Data Pools.
SnapShot Replication Workflow Following the initial creation of the SnapShot pair, which is a one time operation, a SnapShot workflow includes the following basic processes: • Back up a volume • Update the V-VOL • Restore the P-VOL from the V-VOL • Delete the pair, V-VOL, and data pool • Edit the pair and data pool The following sections describe these processes.
4. Existing volumes in the array are listed in the Primary Volume box. Click the button next to the LUN that you want to back up, then click Next. The Prepare Secondary Volume screen displays. 5. The system will create a secondary volume (SnapShot virtual volume) in the array, with the same capacity as the selected P-VOL. In the LUN box, use the default value (if present), or the enter an available logical unit number. Then click Next. The Set Pair Parameters screen displays. 6.
10.In the Group Assignment area, you have the option of assigning the new pair to a consistency group. See Consistency Group (CTG) on page 1-6 for a description. Do one of the following: - If you do not want to assign the pair to a consistency group, leave the Ungrouped button selected. - To create a group and assign the new pair to it, click the New or existing Group Number button and enter a new number for the group in the box.
2. From the Replication tree, select the Local Replication icon. The Pairs screen displays. 3. Select the pair that you want to update and click the Resync Pair button at the bottom of the screen. The operation may take several minutes, depending on the amount of data. 4. When the Resync is completed, click the Split Pair button. This operation is completed quickly. When finished, the V-VOL is updated. • NOTE: Differential data is deleted from the data pool when a V-VOL is updated.
Use the V-VOL for Tape Backup, Testing, Reports, Etc. Your snapshot image (V-VOL) can be used to fulfill a number of data management tasks performed on a secondary server. These management tasks include backing up production data to tape, using the data to develop or test an application, generating reports, populating a data warehouse, and so on. Whichever task you are performing, the process for preparing and making your data available is the same.
Edit Pairs, Data Pool You can edit certain information concerning a pair and a data pool. • For pairs, you can change the name, group name, and copy pace. • For data pools, you can increase the size, edit capacity threshold, and add LUs (volumes). To edit pairs 1. In the Navigator 2 GUI, select the Local Replication icon in the Replication tree view. Advanced users using Navigator 2 CLI, see Changing Pair Information on page A-8. 2. In the GUI, select the pair that you want to edit in the Pairs list. 3.
2. Select the SnapShot Logical Units icon in the tree view. 3. In the Logical Units for Snapshot list, select the V-VOL that you want to delete. 4. Click Delete LU for SnapShot. A message appears. 5. Click Close. The V-VOL is deleted. To delete a data pool 1. Select the Data Pools icon in the tree view. 2. Select a data pool you want to delete in the Data Pool list. 3. Click Delete Data Pool. 4. A message appears. Click Close.
7 Monitoring and Maintenance Your business depends on the data protection provided by SnapShot. It is important that data pool capacity is sufficient to handle the differential data from your P-VOLs. If a data pool should become full, the V-VOLs associated with it are invalidated, and backup data is lost. This chapter provides information and instructions for monitoring and maintaining the SnapShot system.
Monitoring SnapShot The SnapShot data pool must have sufficient capacity to handle the differential data demands placed on it. You must insure that sufficient capacity is always available for the write workload by closely monitoring the following: • Pair status • Data pool usage Monitoring Pair Status To monitor pair status (Advanced users using CLI, see the Storage Navigator Modular 2 Command Line Interface (CLI) User’s Guide.) 1.
Monitoring Data Pool Usage The data pools should be monitored frequently. To monitor data pool usage level (Advanced users using CLI, see the Storage Navigator Modular 2 Command Line Interface (CLI) User’s Guide.) 1. In Navigator 2 GUI, select the desired array, then click the Show & Configure Array button. 2. From the Replication tree, select the Local Replication icon, then select the Setup icon. The Setup screen displays. 3. Select Data Pools. The Data Pools screen displays. 4.
7–4 Monitoring and Maintenance Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
8 Troubleshooting Two types of problem can be experienced with a SnapShot system: pair failure and data pool capacity exceeded. This chapter discusses the causes and provides solutions for these problems.
Pair Failure A pair failure can have two causes: • A hardware failure affecting either the pair volumes or data pool • A data pool whose capacity is exceeded To determine the cause of pair failure 1. Check the status of the data pool whose associated pairs’ status is changed to Failure. For details on checking pair status, see Monitoring Pair Status on page 7-2. 2. If the status of the data pool is POOL FULL, the pair failure is due to capacity is exceeded. 3.
Data Pool Capacity Exceeded When your data pool capacity is exceeded, you must increase the size of the data pool. Most likely, the POOL FULL condition has caused pair failures as well. To address these problems, please see Recovering from Pair Failure Due to POOL FULL on page 8-2.
8–4 Troubleshooting Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
A Operations Using CLI • CAUTION! Storage Navigator 2 CLI is provided for users with significant storage management expertise. Improper use of this CLI could void your Hitachi Simple Modular Storage 100 system warranty. Please consult with your reseller before using CLI. This appendix describes Storage Navigator 2 Command Line Interface (CLI) procedures for Snapshot enabling, configuration and operations.
Enabling and Disabling SnapShot SnapShot is bundled with the Simple Modular Storage system. You must enabled it before using. The following describes the enabling/disabling procedure. • NOTE: The following conditions must be satisfied in order to disable SnapShot: All SnapShot pairs must be released (that is, the status of all LUs are SMPL); All Data Pools must be deleted; All Snapshot Images (VVOL) must be deleted 1.
Snapshot Enable/Disable is complete. Operations for SnapShot Configuration Setting the POOL Up to 64 data pools can be designated for each subsystem, by assigning a logical unit that has been created and formatted. Up to 64 logical units can be assigned to each data pool. The accurate capacity of a data pool cannot be determined immediately after an LU has been assigned. Data pool capacity can only be confirmed approximately 3 minutes per 100 GB.
3. Execute the aupool command to verify that the Data Pool has been created. Refer to the following example. • % aupool –unit subsystem-name –refer -poolno 0 Data Pool : 0 Data Pool Usage Rate: 6% (2.0/30.0 GB) Threshold : 70% Status : Normal LUN Capacity RAID Group RAID Level 100 30.0GB 0 6( 9D+2P) % Type Status SAS Normal 4. When deleting the logical unit set as the Data Pool, it is necessary to delete all Snapshot images (V-VOLs). To delete an existing Data Pool, refer to the following example.
3. To delete an existing SnapShot logical unit, refer to the following example of deleting SnapShot logical unit 1000. When deleting the VVOL, the pair state must be Simplex. • % aureplicationvvol –unit subsystem-name –rm -lu 1000 Are you sure you want to delete the SnapShot logical unit 1000? (y/n[n]): y The SnapShot logical unit has been successfully deleted. % Performing SnapShot CLI Operations The aureplicationlocal command operates SnapShot pair.
Updating SnapShot Logical Unit To update the V-VOL: 1. From the command prompt, register the subsystem to which you want to update the SnapShot pair, then connect to the subsystem. 2. Execute the aureplicationlocal command update the pair. Change the Split status of the Snapshot pair to Paired status using -resync option. Then, change the status to Split using -split option. Refer to the following example.
• % aureplicationlocal –unit subsystem-name –ss –refer Pair name LUN Pair LUN Status Copy Type Group SS_LU0200_LU1001 200 1001 Split(100%) SnapShot ---:Ungrouped % % aureplicationlocal –unit subsystem-name –ss –restore –pvol 200 –svol 1001 Are you sure you want to restore pair? (y/n[n]): y The pair has been restored successfully. % 3. Execute aureplicationlocal to restore the pair. Refer to the following example.
Changing Pair Information You can change the pair name, group name, and/or copy pace. 1. From the command prompt, register the subsystem to which you want to change the SnapShot pair information, then connect to the subsystem. 2. Execute the aureplicationlocal command change the pair information. This is an example of changing a copy pace.
Sample Back Up Script for Windows This section provides sample script for backing a volume on Windows.
A–10 Operations Using CLI Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
B SnapShot Specifications This appendix provides external specifications for SnapShot Snapshot.
General Specifications Table B-1 lists external specifications for SnapShot. • Table B-1: General Specifications Item B–2 Specification Simple Modular Storage model SMS100 (For dual configuration only.) Host interface iSCSI Number of pairs SMS100: 510 (maximum) Command devices Up to 128 per disk subsystem can be set. The command device volume size must be greater than or equal to 33 MB. Unit of pair management Volumes are the target of SnapShot pairs, and are managed per logical unit.
Table B-1: General Specifications Item Specification Reduction of data pool capacity Possible only when all the pairs that use the data pool have been released. Expansion of data pool volume No. Formatting of volumes in a pair No. Pairing with an expanded volume Only P-VOL can be expanded Formatting or expanding VVOL No. Deletion of the V-VOL Only possible when P-VOL and V-VOL are in simplex status and not paired. Swap V-VOL for P-VOL No.
B–4 SnapShot Specifications Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
Glossary This glossary provides definitions for replication terms as well as terms related to the technology that supports your Hitachi Simple Modular Storage 100 array. Click the letter of the glossary section to display that page.
A array A set of hard disks mounted in a single enclosure and grouped logically together to function as one contiguous storage space. asynchronous Asynchronous data communications operate between a computer and various devices. Data transfers occur intermittently rather than in a steady stream. Asynchronous replication does not depend on acknowledging the remote write, but it does write to a local log file.
CLI See command line interface. cluster A group of disk sectors. The operating system assigns a unique number to each cluster and then keeps track of files according to which clusters they use. cluster capacity The total amount of disk space in a cluster, excluding the space required for system overhead and the operating system. Cluster capacity is the amount of space available for all archive data, including original file data, metadata, and redundant data.
configuration definition file The configuration definition file describes the system configuration for making CCI operational in a TrueCopy Extended Distance Software environment. The configuration definition file is a text file created and/ or edited using any standard text editor, and can be defined from the PC where the CCI software is installed. The configuration definition file describes configuration of new TrueCopy Extended Distance pairs on the primary or remote storage system.
D data pool One or more disk volumes designated to temporarily store untransferred differential data (in the local storage system or snapshots of backup data in the remote storage system). The saved snapshots are useful for accurate data restoration (of the P-VOL) and faster remote takeover processing (using the S-VOL). data volume A volume that stores database information. Other files, such as index files and data dictionaries, store administrative information (metadata).
dual copy The process of simultaneously updating a P-VOL and S-VOL while using a single write operation. duplex The transmission of data in either one or two directions. Duplex modes are full-duplex and half-duplex. Full-duplex is the simultaneous transmission of data in two direction. For example, a telephone is a fullduplex device, because both parties can talk at once. In contrast, a walkie-talkie is a half-duplex device because only one party can transmit at a time.
fibre channel A gigabit-speed network technology primarily used for storage networking. firmware Software embedded into a storage device. It may also be referred to as Microcode. full duplex The concurrent transmission and the reception of data on a single link. G Gbps Gigabit per second. granularity of differential data Refers to the size or amount of data transferred to the S-VOL during an update cycle.
iSCSI Internet-Small Computer Systems Interface, a TCP/IP protocol for carrying SCSI commands over IP networks. iSNS Internet-Small Computer Systems Interface, a TCP/IP protocol for carrying SCSI commands over IP networks. L LAN Local Area Network, a computer network that spans a relatively small area, such as a single building or group of buildings. load In UNIX computing, the system load is a measure of the amount of work that a computer system is doing.
M metadata In sophisticated data systems, the metadata -- the contextual information surrounding the data -- will also be very sophisticated, capable of answering many questions that help understand the data. microcode The lowest-level instructions directly controlling a microprocessor. Microcode is generally hardwired and cannot be modified. It is also referred to as firmware embedded in a storage subsystem.
paired volume Two volumes that are paired in a disk array. parity The technique of checking whether data has been lost or corrupted when it's transferred from one place to another, such as between storage units or between computers. It is an error detection scheme that uses an extra checking bit, called the parity bit, to allow the receiver to verify that the data is error free.
R RAID Redundant Array of Independent Disks, a disk array in which part of the physical storage capacity is used to store redundant information about user data stored on the remainder of the storage capacity. The redundant information enables regeneration of user data in the event that one of the array's member disks or the access path to it fails.
S SAS Serial Attached SCSI, an evolution of parallel SCSI into a point-to-point serial peripheral interface in which controllers are linked directly to disk drives. SAS delivers improved performance over traditional SCSI because SAS enables up to 128 devices of different sizes and types to be connected simultaneously. SATA Serial ATA is a computer bus technology primarily designed for the transfer of data to and from hard disks and optical drives.
S-VOL determination Independent of update operations, S-VOL determination replicates the S-VOL on the remote storage system. This process occurs at the end of each update cycle and a pre-determined copy of S-VOL data, consistent with P-VOL data, is maintained on the remote site at all times. T target copy A file, device, or any type of location to which data is moved or copied.
write order guarantee Ensures that data is updated in an S-VOL, in the same order that it is updated in the P-VOL, particularly when there are multiple write operations in one update cycle. This feature is critical to maintain data consistency in the remote S-VOL and is implemented by inserting sequence numbers in each update record. Update records are then sorted in the cache within the remote system, to assure write sequencing.
Index A assessing business needs 2-2 assigning pairs to a consistency group 6-4 B backup script, CLI A-9 C CCI, version 3-2 Command Line Interface changing pair information A-8 creating pairs A-5 enabling and disabling SnapShot A-2 releasing (deleting) pairs A-7 restoring the P-VOL A-6 sample backup script A-9 setting the pool A-3 setting the V-VOL A-4 updating the V-VOL A-6 configuration workflow 5-2 Consistency Groups creating and assigning pairs to using GUI 6-4 creating pairs for using CLI A-8 descrip
O overview 1-1 P pair status definitions 7-2 monitoring 7-2 pairs, assigning to a consistency group 6-4 planning the SnapShot system 2-1 platforms, supported 3-2 Pool Full, recovery from 8-2 P-VOLs and V-VOLs 1-4 R recovering from Pool Full, hardware failure 8-2 releasing (deleting) a pair 6-7 reports, using the V-VOL for 6-6 requirements data pool 2-9 SnapShot system 3-2 Restoring the P-VOL 6-5 resync a pair 6-4 Rolling average 2-6 Simple Modular Storage 3-2 volume pairs creating 6-3 description 1-4 edi
1 Hitachi Simple Modular Storage Copy-on-Write SnapShot User’s Guide
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