Asset ID:	1-71-1001937.1
Update Date:	2012-07-30
Keywords:

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Solution Type  Technical Instruction Sure

Solution  1001937.1 :   Performance Degradation with MPxIO and Symmetric Devices (Sun Storedge[TM] 99xx/3510 and Sun Fire[TM] v880)  


PreviouslyPublishedAs
202693

Applies to:

Sun Storage SAN Foundation Software - Version: 4.0 to 4.4   [Release: 4.0 to 4.0]
Sun Storage 9960 System
Sun Storage 9970 System
Sun Storage 9980 System
All Platforms

Goal

Sequential I/O performance degradation of up to 700% has been seen with Symetric devices connected to the host running Sun StorEdge[TM] Traffic Manager Software (MPxIO) with round-robin load balancing.

Solution

The round-robin method is the default load balancing method when MPxIO is enabled. This method works fine with Asymetric FC (Fibre Channel) devices such as Sun StorEdge[TM] T3, which present LUNs to the host in Active/Passive mode.
The method works counterproductive with Symetric FC Devices like the internal drives of Sun Fire[TM] v880, v1280 or v480, the Sun Storedge[TM] A5x00, 3510, or 99xx array (the 99xx array has a pre-fetch cache alogorithm built into it).

The root cause of the problem is due to the way the MPxIO round-robin method distributes the I/O on 2 or more channels. In the case of an internal disk, or any FC devices in a arbitrated loop, the I/O hits the disk directly from one channel per command. The disk completes the I/O and gets a request from the other channel. This causes the disk to spin (rotational delay) before servicing the request.

The length of delay will vary depending on the number of commands being issued in each path and is very visible with the Sequential I/O. The problem is more visible with Veritas Volume Manager or Solaris Volume Manager, which has stripped volumes with the 16K-interlace factor. This causes an even higher number of commands that need to be sent down to a specific disk, causing high-service times for each command.

The Storedge 99xx array has its own pre-fetch cache algorithm, which in some cases, may cause performance degradation.

The solution is a new method of load-balancing; the "logical block" method.
This method uses a region size (specified in the conf file of 16, 32 ....), then routes all I/Os, starting within a certain 64K range, through the same path. I/Os that start within other 64K ranges on the disk will be routed through a different path. This way, the disk can catch the stream  I/O better, which improves the performance.

Below are basic changes in the scsi_vhci.conf for using the "logical block" method. Document 1004918.1 describes the new load balancing method in detail.

This is provided through the new property,
"device-type-mpxio-options-list".

device-type-mpxio-options-list=
"device-type=SUN     SENA", "load-balance-options=logical-block-options";
"device-type=SEAGATE ST373307FSUN72G",
"load-balance-options=logical-block-options1",
"device-type=HITACHI OPEN-L*4    -SUN",
"load-balance-options=logical-block-options2",
"device-type=SUN     T300", "load-balance-options=logical-block-options1";
logical-block-options="load-balance=logical-block",  "region-size=15";
logical-block-options1="load-balance=logical-block", "region-size=18";
logical-block-options2="load-balance=logical-block", "region-size=32";

Note: The Product ID in the device-type string should start at the "9th" character. Otherwise, it will use the default round-robin load balancing method.

This logical-block method is available beginning with SAN 4.4

Product
Sun StorageTek 9980 System
Sun StorageTek 9970 System
Sun StorageTek 9960 System
Sun StorageTek 9910
Sun StorageTek 9900V Series Array
SAN drivers, Mpxio

Keywords: MPxIO, HDS, SDS, VxVM, Performance, v880, v1280, v480, SE9900, 9910, 9960, 9970, 9980, hitachi

Internal section

Previously Published As 76504




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