multipathd: failed setting max_sectors_kb on sdc : Invalid argument

Environment

• Red Hat Enterprise Linux

Issue

• Unable to set max_sectors_kb in multipath.conf:

    Nov 26 10:56:16 multipathd: failed setting max_sectors_kb on sdc : Invalid argument 
    Nov 26 10:56:16 multipathd: failed setting max_sectors_kb on sdi : Invalid argument
    Nov 26 10:56:16 multipathd: failed setting max_sectors_kb on sde : Invalid argument
  

Resolution

• Set the max_sectors_kb to a number below both max_hw_sectors_kb and max_dev_sectors.

Root Cause

• The max_sectors_kb was set to a value higher than max_dev_sectors.

Diagnostic Steps

• Check the device's max_hw_sectors_kb and ensure that max_sectors_kb is lower:

    [root@host ~]# cat /sys/block/sdc/queue/max_hw_sectors_kb 
    32767
  

• Check max_dev_sectors via sg_vpd command and ensure that max_sectors_kb is lower:

Note  If VPD page 0xB0 (SCSI Block Limits) is not supported by the device, then skip this check based upon the Maximum transfer length value.

[root@host ~]# sg_vpd -p 0xb0 /dev/sdc  
Block limits VPD page (SBC):
  Write same no zero (WSNZ): 1
  Maximum compare and write length: 1 blocks
  Optimal transfer length granularity: 8 blocks
  Maximum transfer length: 2048 blocks     <======
  Optimal transfer length: 128 blocks
  Maximum prefetch length: 0 blocks
  Maximum unmap LBA count: 0
  Maximum unmap block descriptor count: 0
  Optimal unmap granularity: 0
  Unmap granularity alignment valid: 0
  Unmap granularity alignment: 0
  Maximum write same length: 0x4000 blocks

• So, the highest allowed value for max_sectors_kb here would be 1024KiB as shown below:

    2048 blocks (logical sectors)  x 512 bytes per disk block = 1048576 bytes / 1024 bytes per KiB = 1024KiB
    1024 max_sectors_kb x 1024 bytes per KiB = 1048576 bytes
  

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