POWERVAULT MD3000 AND MD3000i ARRAY TUNING BEST PRACTICES dell.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices DISCLAIMER THIS WHITE PAPER IS FOR INFORMATIONAL PURPOSES ONLY, AND MAY CONTAIN TYPOGRAPHICAL ERRORS AND TECHNICAL INACCURACIES. THE CONTENT IS PROVIDED AS IS, WITHOUT EXPRESS OR IMPLIED WARRANTIES OF ANY KIND. For more information, contact Dell™. Information in this document is subject to change without notice. http://www.dell.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices Table of Contents 1 AUDIENCE AND SCOPE .............................................................................................................................. 4 2 PERFORMANCE TUNING OVERVIEW .......................................................................................................... 4 2.1 2.2 COMPONENTS THAT INFLUENCE STORAGE PERFORMANCE ..................................................................................
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices 1 Audience and Scope This document is intended to guide MD3000 and MD3000i customers through the advanced processes behind tuning their storage array to best suit their individual needs. Presented within are the best practices that must be observed in performance tuning a first generation firmware (06.XX.XX.XX) and second generation firmware (07.XX.XX.XX) storage array.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices The answers include: • “It depends…” There are no absolute answers. Each environment is unique and the correct settings depend on the unique goals, configuration, and demands for the specific environment. • “Actual mileage may vary.” Results vary widely because conditions vary widely.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices • Profile of mean I/O direction; this is usually the ratio of Reads to Writes 4 Configuring the MD3000/MD3000i There are two ways to configure the MD3000 and MD3000i storage systems. The most common and easiest method is using the MDSM. The MDSM allows automatic configuration settings that provide reasonable configurations with little knowledge of performance tuning required.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices Physical disk cost is not the only factor that influences the decision on which RAID level is most appropriate for a given application. The performance of a chosen RAID level is heavily interdependent on characteristics of the I/O pattern as transmitted to the storage array from the host(s). With I/O patterns involving write operations, when an I/O burst exceeds 1/3 of available cache memory in size, it should be considered a long I/O.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices 4.1.1 Selecting a RAID Level - High Write Mix Scenario In random I/O applications with a >10% mix of write operations and a low degree of burstiness, RAID 1/10 provides the best overall performance for redundant disk groups. RAID 1/10 performance can be >20% better than RAID 5 in these environments, but has the highest disk cost; for instance, more physical disks must be purchased.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices • To optimize for data transfer rate, multiply the number of physical data disks by the segment size to equal the I/O size. However, there are always exceptions. For small/medium I/Os care should be taken to avoid splitting up the I/O in such a way that an even smaller I/O is sent to the disk drives. Please note that data disks do not include parity or mirror disks used in a RAID set.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices traffic virtual disks share a disk group, even with purely sequential usage models, the disk group I/O behavior becomes increasingly random, lowering overall performance. Additionally, when a disk group must be shared, the most heavily trafficked virtual disk always should be located at the beginning of a disk group. 4.4 Virtual Disk Ownership The Dell™ MDSM can be used to automatically build and view virtual disks.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices first 128KiB of an I/O is written to the first drive, the next 128KiB to the next drive, and so on with a total stripe size of 512KiB. For a RAID 1, 2 + 2 virtual disk group, 128KiB would be written to each of the two drives (and same for the mirrored drives). If the I/O size is larger than this (the number of physical disks multiplied by a 128KiB segment), this pattern repeats until the entire I/O is complete.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices 4.6 Cache Settings Read-ahead cache can be configured in the MDSM and through the CLI. The MDSM has only the defaults to work with, while the CLI can fully configure the read-ahead cache. Additionally, the global cache block size for read and write cache can be adjusted through the CLI. Please refer to the Dell™ PowerVault™ Modular Disk Storage Manager CLI Guide on the Dell™ technical support site (http://support.dell.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices 4.6.3 Setting the Storage Array Cache Block Size Configured through the CLI – This command is available at the storage array level and effects all virtual disks and disk-groups. Cache Block Size – Cache Block Size refers to the way cache memory is segmented during allocation and affects all virtual disks in an array. On the MD3000 and MD3000i, settings of 4KiB and 16KiB are available with 4KiB being the default.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices 4.7 Tuning Using Array Performance Data 4.7.1 Collecting Performance Statistics The stateCaptureData.txt and performanceStatistics.csv files, which are available through the MDSM, Support tab as part of a Technical Support Bundle, provide valuable statistical data in an easy-to-read format. The following section shows some sample data from the stateCaptureData.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices Figure 2: First Generation Firmware - RAID Level. File: stateCaptureData.txt Virtual Disk Unit 0 Configuration Volume Type: 13+1 RAID 5 User Label: MyRAID5_1 Block Size: 512 bytes Large IO: 4096 blocks Segment Size: 256 blocks Stripe Size: 3328 blocks ... IO Statistics: small small reads writes requests 2028332119 147699066 blocks 3091968111 2518067526 avg blocks 4 17 IO pct. 93.21% 6.78% reads writes write algorithms large reads 0 0 0 0.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices to how tightly the variance of sequential or random data access is contained within the volume. This can be purely random across an entire virtual disk, or random within some bounds, such as a large file stored within a virtual disk compared to large non-contiguous bursts of sequential data access randomly distributed within some bounds. Each of these is a different I/O pattern, and has a discrete case to be applied when tuning the storage.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices In the first generation of firmware (see Figure 5), this can be determined from the ‘Avg. Blocks’ row which represents the average I/O block size encountered. In Generation One, the ‘Large IO’ field denotes a 4096 block or 2MiB size with zero registered Large Reads or Writes during the sample period. Any single host received I/O greater than the Large I/O size is broken down into chunks less than or equal to the stated Large I/O value.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices In addition, the stateCaptureData.txt file provides a more granular method for determining the distribution of I/O within stripes and segments. In Figure 7 and Figure 8, item 1 is the number of full stripes read and written, and item 2 indicates the number of full clusters or segments read or written.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices Figure 8: Second Generation Firmware– Stripe distribution. File: stateCaptureData.txt Volume 0 Attributes: Volume Type: RAIDVolume User Label: MyRAID10_One ... BlockSize: 512 bytes 3. LargeIoSize: 4096 blocks ... Perf. Stats: Requests Blocks Reads 67456452 5943724625 Writes 27283249 1144902648 Large Reads 0 0 Large Writes 0 0 1. Total 94739701 7088627273 ...
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices RMW, or Read-Modify-Write, is the second-best write algorithm available for RAID 5 and 6. A RMW occurs when a quantity of bits, smaller or equal to an individual segment are modified. This constitutes a two-read operation in RAID 5 and a three-read operation in RAID 6, with one of the segments being modified, and the parity drive(s) are read in.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices Figure 10: Second Generation Firmware - Write Algorithms Volume 1 Attributes: Volume Type: RAIDVolume User Label: MyRAID5vd ... BlockSize: 512 bytes LargeIoSize: 4096 blocks ... Perf. Stats: Requests Blocks Reads 577761063 1155647889 Writes 82542765 175687877 Large Reads 0 0 Large Writes 0 0 Total 660303828 1331335766 ...
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices For a complete list of commands and instructions on using the CLI Performance Monitor, refer to the Dell™ PowerVault™ Modular Disk Storage Manager CLI Guide on http://support.dell.com/manuals. 4.9 Other Array Considerations 4.9.1 Global Media Scan Rate Use the Tools tab to change/set the Media Scan settings in the MDSM.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices 5 Considering the Host Server(s) 5.1 Host Hardware Platform 5.1.1 Considering the Server Hardware Architecture Available bandwidth depends on the server hardware. The number of buses adds to the aggregate bandwidth, but the number of HBAs sharing a single bus can throttle the bandwidth. Additionally, some server hardware has slower-speed PCIE ports (4x) as well as high-speed ports (8x).
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices Figure 11: MD3000i Advanced IPv4 Settings: VLAN, QOS, Jumbo Frames Support 5.1.3 Sharing Bandwidth with Multiple SAS HBAs Each SAS wide port includes four full duplex serial links within a single connector. The individual SAS 1.1 links run a maximum speed of 3Gb/s. A single path is used as the primary path to a connected device — the second, third, and fourth paths are used as overflow, when concurrent I/Os overload the primary channel.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices used at certain times, providing a point-to-point raw wire speed of up to 12Gb/s. Please note that this raw speed does not take into account the transmission overhead or device spenditures on either side of the SAS wide link and is purely a cached I/O operation. Additionally, care must be taken of which buses are being used within the host. Installing the HBAs that use the same bus will hamper data transfer rate.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices Microsoft provides the diskpar.exe utility as part of the Microsoft Windows 2000 Resource Kit, which was renamed to diskpart.exe in Microsoft Windows 2003 and later. Microsoft has a KB article 929491 covering this, and Dell™ always recommends checking for proper partition alignment to the stripe size of assigned virtual disks.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices Appendix A: Obtaining Additional Performance Tools Table 3 shows a number of widely available tools, benchmarks, and utilities. Some of these tools are produced by non-profit organizations and are free. Table 3: Performance Tools Name Description Platform Available From IOBench I/O data rate and fixed workload benchmark Unix/Linux http://www.acnc.com/benchmarks.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices Appendix B: System Troubleshooting For information about troubleshooting MD3000 and MD3000i storage arrays, refer to the “Troubleshooting Problems” chapter of the Dell™ PowerVault™ Modular Disk Storage Manager User’s Guide. Go to: MD3000: http://support.dell.com/support/edocs/systems/md3000/en/index.htm MD3000i: http://support.dell.com/support/edocs/systems/md3000i/en/index.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices Appendix C: References Dell™ PowerVault™ Modular Disk Storage Manager CLI Guide, http://support.dell.com/support/edocs/systems/md3000/en/index.htm Dell™ PowerVault™MD3000, http://support.dell.com/support/edocs/systems/md3000/en/index.htm PowerVault MD3000i SAN Array for Storage Consolidation, http://www.dell.com/content/products/productdetails.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices Appendix D: Glossary of Terms Term Burstiness Controller Saturation GiB HBA HDD Interposer iSCSI KiB Kibibyte Long I/O MD3000 MD3000i MDSM MiB NIC NL-SAS Definition A data traffic property defined as the ratio of the peak I/O rate to the average I/O rate; in this case, the mean duty cycle exhibited by I/O transmitted or received from a storage array. Burstiness is adopted from its common usage in describing network workloads.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices Term RAID RAID 0 RAID 1/10 RAID 5 RAID 6 RPA RMW RMW2 SAS SATA Saturation SCSI Definition directly on the drive in lieu of using an SATA interposer. Redundant Array of Inexpensive Disks RAID Level 0; RAID 0 is a striped set with no redundant information. It is effectively a fully degraded RAID set with no disk redundancy overhead.
Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices Term Segment Short I/O SQL Stripe Definition by t10.org A segment is the data written to one drive in a virtual disk group stripe before writing data to the next drive in the virtual disk group stripe. Any I/O that consumes less that 1/3 of available cache memory that can be handled within cache, effectively a cached operation. Structured Query Language; flexible markup language for computer databases maintained by ANSI and ISO.
