On Sun, 2008-06-29 at 01:36 -0500, Mike Christie wrote:
> Nicholas A. Bellinger wrote:
> > Hi Mike!
> > 
> 
> Hey, looks like you doing some more cool stuff. Don't you have a job 
> where you have to hack on boring stuff like the rest of us :)
> 

What Jerome said. :-)

> 
> > On Sat, 2008-06-28 at 15:33 -0500, Mike Christie wrote:
> >> What version of open-iscsi and kernel are you using? And are you using 
> >> the kernel modules with open-iscsi or the ones that come with the kernel?
> >>
> > 
> > Whoops, forgot to include that tid-bit:
> > 
> > open-iscsi: 2.0.730-1etch1
> > 
> > kernel: I am using v2.6.22.19-kdb, and Jerome is using
> > v2.6.22-4-vserver-amd64
> > 
> 
> Ah if your disk are using write back cache then you are going to hit 
> some problems. So if you see this in /var/log/messages when you loging:
> 
> kernel: sd 9:0:0:1: [sdb] Write cache: enabled,
> 
> then later when you run iscsiadm to log out you see:
> 
> kernel: sd 9:0:0:1: [sdb] Synchronizing SCSI cache
> 
> Then you are going to hit problems due to the scsi sysfs interface 
> changing on us. iscsiadm is going to hang. IO is going to hang. You 
> basically have to reboot the box by hand.
> 

Yep, so the LIO-CORE does NOT emulate Write Cache Enable (although there
is some Read Cache code :-) bit in the caching mode page in the virtual
storage object case (IBLOCK, FILE, etc).  We are using the LIO-Core
IBLOCK plugin for export DRBD's struct block_device, which uses the
generic emulation of MODE_SENSE*, which leaves buf[2] untouched in
caching mode page.  

For the PSCSI subsystem plugin, these mode pages obviously come from the
underlying hardware.  I even recall that libata does emulate this down
to SATA/PATA bits for us. (thanks jgarzik and co)  

On a related note, did you and Tomo ever get around to implement
write/read caching emulation in STGT for virtual devices..?  Its
definately something that is on my long term list for doing generically
amoungst virtual devices in LIO-Core v3.x.

Many thanks for your most valuable of time,

--nab

> > 


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