open-iscsi queue_depth

[Pasi Kärkkäinen]

Hello list!

Just to check, can you change queue depth of open-iscsi device in the normal
way:

# cat /sys/block/sda/device/queue_depth
32

# echo 128 > /sys/block/sda/device/queue_depth

I'm asking because if I remember correctly there was also an option for this
in iscsid.conf.. or does it just set the default sysfs device queue_depth
value?

Second question would be: Is queue_depth value of _open-iscsi_ device just
like queue_depth for local RAID card? Possibly having big effect to
performance you get depending of the storage adapter/raid/disks.

Thanks!

-- Pasi

[Mike Christie]

Pasi Kärkkäinen wrote:
> Hello list!
>
> Just to check, can you change queue depth of open-iscsi device in the normal
> way:
>
> # cat /sys/block/sda/device/queue_depth
> 32
>
> # echo 128 > /sys/block/sda/device/queue_depth

Yeah.

>
> I'm asking because if I remember correctly there was also an option for this
> in iscsid.conf.. or does it just set the default sysfs device queue_depth
> value?

If you set node.session.queue_depth in iscsi.conf it sets the
cmd_per_lun (see /sys/class/scsi_host/hostX/cmd_per_lun) and that is
used as the initial queue depth for the device when it is first created.
It is basically like doing "echo 128 >
/sys/block/sda/device/queue_depth" from userspace when the device is
first created.

And if you set node.session.queue_depth, you can still override it for a
specific device by just writing to /sys/block/sda/device/queue_depth.

>
> Second question would be: Is queue_depth value of _open-iscsi_ device just
> like queue_depth for local RAID card? Possibly having big effect to

Yeah, queue_depth is just the scsi/block device queue depth like you see
for a local scsi disk. There is nothing iscsi specific about the value.

[Pasi Kärkkäinen]

On Thu, Nov 08, 2007 at 12:30:33AM -0600, Mike Christie wrote:
>
> Pasi Kärkkäinen wrote:
> > Hello list!
> >
> > Just to check, can you change queue depth of open-iscsi device in the normal
> > way:
> >
> > # cat /sys/block/sda/device/queue_depth
> > 32
> >
> > # echo 128 > /sys/block/sda/device/queue_depth
>
> Yeah.
>

OK.

> >
> > I'm asking because if I remember correctly there was also an option for this
> > in iscsid.conf.. or does it just set the default sysfs device queue_depth
> > value?
>
>
> If you set node.session.queue_depth in iscsi.conf it sets the
> cmd_per_lun (see /sys/class/scsi_host/hostX/cmd_per_lun) and that is
> used as the initial queue depth for the device when it is first created.
> It is basically like doing "echo 128 >
> /sys/block/sda/device/queue_depth" from userspace when the device is
> first created.
>
> And if you set node.session.queue_depth, you can still override it for a
> specific device by just writing to /sys/block/sda/device/queue_depth.
>

OK.

>
>
> >
> > Second question would be: Is queue_depth value of _open-iscsi_ device just
> > like queue_depth for local RAID card? Possibly having big effect to
>
> Yeah, queue_depth is just the scsi/block device queue depth like you see
> for a local scsi disk. There is nothing iscsi specific about the value.
>

Yep, that's what I thought.

Thanks for the reply!

-- Pasi