elevator=deadline

[charl]

 29937    0 -rw-r--r--   1 root     root         4096 Mar  7 16:27 ./devices/virtual/block/VxVM3000/queue/scheduler
 30024    0 -rw-r--r--   1 root     root         4096 Mar  7 16:27 ./devices/virtual/block/VxVM4000/queue/scheduler
 30128    0 -rw-r--r--   1 root     root         4096 Mar  7 16:27 ./devices/virtual/block/VxVM4001/queue/scheduler
 31259    0 -rw-r--r--   1 root     root         4096 Mar  5 11:51 ./devices/virtual/block/VxDMP2/queue/scheduler
 31642    0 -rw-r--r--   1 root     root         4096 Mar  5 11:51 ./devices/virtual/block/VxDMP3/queue/scheduler
 31780    0 -rw-r--r--   1 root     root         4096 Mar  5 11:51 ./devices/virtual/block/VxDMP4/queue/scheduler
 31918    0 -rw-r--r--   1 root     root         4096 Mar  5 11:51 ./devices/virtual/block/VxDMP5/queue/scheduler
 32056    0 -rw-r--r--   1 root     root         4096 Mar  5 11:51 ./devices/virtual/block/VxDMP6/queue/scheduler
 32194    0 -rw-r--r--   1 root     root         4096 Mar  5 11:51 ./devices/virtual/block/VxDMP7/queue/scheduler
 32301    0 -rw-r--r--   1 root     root         4096 Mar  5 11:51 ./devices/virtual/block/VxDMP8/queue/scheduler
 32439    0 -rw-r--r--   1 root     root         4096 Mar  5 11:51 ./devices/virtual/block/VxDMP9/queue/scheduler
 32546    0 -rw-r--r--   1 root     root         4096 Mar  5 11:51 ./devices/virtual/block/VxDMP10/queue/scheduler
 21089    0 -rw-r--r--   1 root     root         4096 Mar  7 16:27 ./devices/pci0000:00/0000:00:09.0/0000:09:00.0/host0/rport-0:0-2/target0:0:0/0:0:0:0/block/sda/queue/scheduler
 20640    0 -rw-r--r--   1 root     root         4096 Mar  7 16:27 ./devices/pci0000:00/0000:00:09.0/0000:09:00.0/host0/rport-0:0-2/target0:0:0/0:0:0:1/block/sdb/queue/

chrbl357:/sys # cat ./devices/virtual/block/VxVM3000/queue/scheduler
[noop] deadline cfq
chrbl357:/sys # cat ./devices/virtual/block/VxVM4000/queue/scheduler
[noop] deadline cfq
chrbl357:/sys # cat ./devices/virtual/block/VxDMP2/queue/scheduler
none
chrbl357:/sys # cat ./devices/virtual/block/VxDMP7/queue/scheduler
none
chrbl357:/sys # cat ./devices/pci0000:00/0000:00:09.0/0000:09:00.0/host0/rport-0:0-2/target0:0:0/0:0:0:0/block/sda/queue/scheduler
[noop] deadline cfq
chrbl357:/sys #
 

We change the scheduler option down the "/sys/block" path. In this instance we change it to noop but more often it is changed to deadline. However am confused about the scheduler file under VxVM3000 or VxDMPx. How does this interact with the block device scheduler settings?

[Max_McKinney · Accepted solution]

Hi Charl,

VxVM is hard coded to use the deadline scheduler for VxVM#### volume devices. If you specify a different scheduler in your grub.cfg, it still won't change on the VxVM volume devices.

The only way to get it to change is to modify the /sys/block device, which it looks like you have already done. However, this only works temporarily. Once you reimport the DG it will go back to deadline.

Because the VxVM volume is not a physical device, changing the scheduler should not have a very big impact on performance. The IO sent to the VxVM volume device is passed down to the underlying physical devices which should be using whatever scheduler was specified in grub.

Bottom line is that there is no easy way to permenantly change the scheduler for VxVM volume devices. The scheduler for the underlying physical device is what really matters.

Best Regards,
Max

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