Write back cache

[galitz]

Hello,

I am connecting to iSCSI targets on a QNAP TS-439U. They connect as
write-through cache enabled, but I cannot seem to tune the cache on
the QNAP side. Is there a way to enable/configure write back cache on
the Linux initiator side?

I am actually doing this via XenServer, but they seem to be using
standard open-iscsi from what I can tell.

Thanks,
Geoff

[Mike Christie]

galitz wrote:
> Hello,
>
> I am connecting to iSCSI targets on a QNAP TS-439U. They connect as
> write-through cache enabled, but I cannot seem to tune the cache on
> the QNAP side. Is there a way to enable/configure write back cache on
> the Linux initiator side?
>

You might want to post to linux-kernel or linux-scsi list. The iscsi
initiator does not control this, but I think there are some scsi or
block layer tools that can do it if the target/disk supports it.

[Geoff Galitz]

> You might want to post to linux-kernel or linux-scsi list. The iscsi
> initiator does not control this, but I think there are some scsi or
> block layer tools that can do it if the target/disk supports it.

I'll do that. I did try to use sgmode to enable this, but that just did not
work.

-geoff



---------------------------------
Geoff Galitz
Blankenheim NRW, Germany
http://www.galitz.org/
http://german-way.com/blog/

[Ulrich Windl]

On 15 Dec 2009 at 10:32, Geoff Galitz wrote:

>
> > You might want to post to linux-kernel or linux-scsi list. The iscsi
> > initiator does not control this, but I think there are some scsi or
> > block layer tools that can do it if the target/disk supports it.
>
> I'll do that. I did try to use sgmode to enable this, but that just did not
> work.

Actually I think if you can't do it on the remote end (i.e. target), the initiator
will also fail, because iSCSI just transports the request to the target.

Regards,
Ulrich

[Mike Christie]

I think Geoff and I were talking about using a tool like from sg3_utils,
which sends scsi commands to the target. The scsi commands can change
settings or do things like fail over a lun/controller. You are right
though. The iscsi stuff has nothing to do with it. The scsi commands are
just sent over iscsi. And it would be strange not to have a user
friendly interface on the target, but allow you to do it with sg utils.