scsi max q depth value

[krissh89]

Hi

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]

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.

[krissh89]

HI 

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]

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
/dev/rchgr/autoch1:1
/dev/pt/pt1:1
/dev/rdisk/disk16:8
/dev/rdisk/disk20:8
/dev/rdisk/disk7:8
/dev/rdisk/disk41:8
/dev/rdisk/disk11:8
/dev/rdisk/disk9:1
/dev/rtape/tape2_BEST:1
/dev/rdisk/disk12:1
/dev/rtape/tape4_BEST:1