PS Series iSCSI Volume Connection Count Maximum Characterization Dell EMC Engineering November 2016 A Dell EMC Technical White Paper
Revisions Date Description February 2012 Initial publication March 2012 Updates to section 5 December 2016 Updated to reflect industry changes Acknowledgements Updated by: David Glynn The information in this publication is provided “as is.” Dell Inc. makes no representations or warranties of any kind with respect to the information in this publication, and specifically disclaims implied warranties of merchantability or fitness for a particular purpose.
Table of contents Revisions.............................................................................................................................................................................2 Acknowledgements .............................................................................................................................................................2 1 2 Introduction ...................................................................................................................
1 Introduction This section describes the intended audience of the paper, explains the purpose of the paper, and presents a summary of findings. 1.1 Audience The information in this technical paper is intended for anyone designing, quoting, deploying, administering, or scaling out a Dell EMC PS Series storage solution. 1.
2 Overview This section provides an overview of the PS Series SAN architecture and gives specific information on when and how iSCSI connections are made by common storage initiators. 2.1 PS Series SAN architecture The PS Series SAN architecture enables simultaneous access from multiple storage initiators to multiple storage targets distributed across multiple peer storage (PS) member arrays using iSCSI, the Internet Protocol (IP) based storage networking standard.
2.3.1 Native MPIO modules Table 2 shows the number of iSCSI connections created by default in Windows Server and ESXi when using the native MPIO modules and software initiator of each OS to connect to a storage target. Additional paths may be configured manually depending on the OS. Note that the connection count is not affected by the number of member arrays (and volume slices). In ESXi, one iSCSI connection is made for each VMkernel port assigned to the software initiator.
for a period of time the volume will reside on higher number of member arrays. If the storage initiator is running a PS Series MPIO module that is dynamically tracking volume slice quantity and location, then the total number of iSCSI connections will temporarily increase before returning to the original quantity.
3 Performance testing This section covers in greater detail the methods and results of the testing used to determine the effect of larger numbers of iSCSI connections on storage pool performance. 3.1 Test environment In order to determine whether or not SAN performance is affected as the total number of storage pool iSCSI connections increases towards the officially supported maximum, we used the performance tool Vdbench to capture throughput, IOPS, and application latency.
Test 1: 8K, random I/O, 67% read workload configurations at 510, 750, and 1020 iSCSI connections during an 8K, random I/O, 67% read workload. Figure 1 shows the IOPS and response time as a percentage of the baseline value measured at 510 iSCSI connections by Vdbench for one-, two- and three-member array storage pools.
Test 2: 64K, sequential I/O, write workload configurations at 510, 750, and 1020 iSCSI connections during a 64K, sequential I/O, write workload. Overall performance remains consistent as the number of iSCSI connections increase.
Test 3: 256K, sequential I/O, read workload configurations at 510, 750, and 1020 iSCSI connections during a 256K, sequential I/O, read workload. Overall performance remains consistent as the number of iSCSI connections increase.
4 Availability testing This section describes the test environment used to determine if SAN availability was affected when operating near the maximum number of iSCSI connections to the storage pool. 4.
5 Recommended practices The following section explains how to calculate the total number of iSCSI connections to expect from a given PS Series SAN configuration along with options for reducing the total number of connections. 5.1 Calculating total iSCSI connections By default, the PS Series MPIO module creates two connections per volume slice to a storage volume, up to a maximum of six connections.
5.2 Tips for reducing iSCSI connections There are several ways to reduce the number of overall iSCSI connections required for a given SAN installation. The simplest action, which does not require any change to the underlying SAN design or administrative strategy, is to change the Max Sessions per Volume Slice setting of the PS Series MPIO module from two to one on each storage initiator, effectively cutting in half the number of iSCSI connections that will be required for a given SAN configuration.
A Hardware diagram A hardware diagram of the servers, switches, and storage used in the test environment 15 PS Series iSCSI Volume Connection Count Maximum Characterization | BP1023
B Logical diagram The following diagram shows the allocation of the networking resources in the test environment.
C Solution infrastructure Table 4 provides a detailed inventory of the hardware and software configuration in the test environment. Configuration for test environment Hardware components Description Windows Server 2008 R2 server Dell EMC PowerEdge R610 Server: Windows Server 2008 R2 SP1 BIOS version: 3.0.0 2 x Intel® Xeon® Processor X5650 32GB RAM PERC 6/i – v1.22.12-0952 2 x Fujitsu 300GB SAS – vD809 1 x Intel VT Quad 1GbE NIC – driver v11.4.7.0 EqualLogic Host Integration Toolkit v3.5.
D Vdbench parameters Vdbench workloads were executed using the following parameters in the parameter file, where N is the number of iSCSI volumes under load. Common parameters: hd=default hd=one,system=localhost iSCSI volumes: sd=sd1,host=*,lun=\\.\PhysicalDrive1,size=10240m sd=sd2,host=*,lun=\\.\PhysicalDrive2,size=10240m ... sd=sd3,host=*,lun=\\.\PhysicalDriveN,size=10240m 8K, 67% read, random I/O workload: wd=wd1,sd=(sd1-sdN),xfersize=8k,rdpct=67 64K, 100% write, sequential I/O workload: wd=wd1,sd=(sd1-
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