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scsi max q depth value

Occasional Advisor

scsi max q depth value



When I run scsimgr get_attr -D /dev/rdisk/disk##


I could see the max_q_depth paramater is set to 8.

OS version : hpux 11 iv3

disk type : Virtual scsi disk

storage :3par


both vsp and guest has set a value of 8.


so which means 8 I/O process can be queued to that disk.


1.How this value is measured is it in 8 KB, 8MB, 8GB

2.to increae the value what are all the others details I have to check.HOw can i calculate the larger value.



Bill Hassell
Honored Contributor

Re: scsi max q depth value

The max_q_depth is the number of requests that can be queued up at the same time. 8 is fairly low for modern disk arrays. You could try setting it to 64 or even 128 but a lot depends on how the array handles large queues.

Bill Hassell, sysadmin
Occasional Advisor

Re: scsi max q depth value



In other server I could see that max-q-depth value is set to 32.


name = max_q_depth
current = 32
default = 32
saved =



By defult I could see the value is set to 32.


I could change it using  set_attr and save_attr  to higher values but I need to know how the default value is set to 32.


Is it  default value set from Storage End or OS end ?



Bill Hassell
Honored Contributor

Re: scsi max q depth value

The default value is reported from the driver, but there seems to be a connection from the driver to storage that can change the default. Here is a way to see all the current values:

# scsimgr -p get_attr all_lun -a device_file -a max_q_depth

Bill Hassell, sysadmin