I/O is not sent down all configured paths when using Storage Foundation for Windows (SFW) DMP DSM (MPIO) Multipathing in an Active/Active configuration with an EMC Symmetrix array

Article:TECH191542  |  Created: 2012-06-23  |  Updated: 2012-06-23  |  Article URL http://www.symantec.com/docs/TECH191542
Article Type
Technical Solution


Environment

Issue



When using Storage Foundation for Windows (SFW) DMP DSM Multipathing, certain configurations can result in I/O failing to be sent down all configured paths. This may be seen as an I/O performance issue, but in order to determine if this issue is the cause, the vxdmpadm command can be used to report I/O statistics on all paths for the harddisk specified.

The command to run is: vxdmpadm iostat showdevice interval=5 harddiskx

* where x is the harddisk# of a disk in the array that currently has Active I/O

                               OPERATIONS/SEC    BYTES/SEC
DISK            PATHNAME        READS   WRITES  READS   WRITES

Harddisk2       Path 1-0-0      0       4       0       194150
Harddisk2       Path 2-0-0      0       4       0       231014
Harddisk2       Path 3-0-0      0       4       0       222822
Harddisk2       Path 4-0-0      0       4       0       145817
Harddisk2       Path 5-0-0      0       0       0       000000
Harddisk2       Path 6-0-0      0       0       0       000000
Harddisk2       Path 7-0-0      0       0       0       000000
Harddisk2       Path 8-0-0      0       0       0       000000


Here we can clearly see that I/O is only being sent down 4 of 8 paths


Environment



This issue will only be seen in large environments where there are 32+ unique paths to an EMC Symmetrix Storage Array. This would mean that there would be multiple subsets of disks from the same array that are configured down different paths:

Example:

Disks1-10 = Paths1-8
Disks11-20 = Paths 9-16
Disks 21-30 = Paths 17-24
Disks 31-40 = Paths 25-32
Disks 41-50 = Paths 33-40

Even though each device only has 8 paths to storage (which is below the 16 path limitation), there was an issue in the product where it was limiting the total number of paths per array to 32. Since there are 40 paths in this configuration, 8 paths would never validate with the MPIO framework, so these paths would be unuseable.


Cause



SFW DMP DSMs restrict the total # of paths to a single disk device to 32 (Note: Microsoft's MPIO limitiation is 16 paths currently); however, due to an issue is the DSM, it was limiting the total # of paths to the entire array instead of each individual disk.


Solution



This issue has been identified and a private fix is available from Symantec Enterprise Technical Support. To obtain the private fix, contact Symantec Support and reference this TechNote during the call. A support representative will be available to assist in troubleshooting this issue.

If it is determined that the private fix addresses the problem, the support representative will further assist in obtaining the private fix. For a complete list of Symantec Enterprise Technical Support contact numbers, go to http://www.symantec.com/enterprise/support/index.jsp

This fix is available for the following SFW / SFW-HA versions:

SFW 5.1 SP1
SFW 5.1 SP2
SFW 6.0

SFW-HA 5.1 SP1
SFW-HA 5.1 SP2
SFW-HA 6.0

Note: This fix specifically addresses the problem identified above. It has not been fully tested and should be applied in a test environment before placing into production. If the systems are not critically impaired, it is recommended to delay the installation of this private fix until the next scheduled maintenance release. Before applying this private fix, systems may be required to be upgraded to the latest code base. The support representative will help in determining the best course of action.


Supplemental Materials

SourceETrack
Value2711792
Description

DMP RR is only using 4 of the 8 paths presented



Article URL http://www.symantec.com/docs/TECH191542


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