Re: experience with gnbd

[Jacob Gorm Hansen <jacobg@diku.dk>]

Ian Pratt wrote:
> In the last couple of days we've been playing around with gnbd as
> an alternative to iSCSI, as we found that the performance of the
> current cisco linux iSCSI implementation was fairly awful talking
> to our NetApp hardware target.

Cool, need to try this as an alternative to the 'iscsitarget' from 
sourceforge, even though that also works fairly well, serving disks from 
dom0.

What kind of performance improvement did you experience? This is not 
just due to the NetApp filer being on a separate network with a router 
or firewall in between (if I recall correctly)?

> I haven't tried it, but the csnap writeable snapshot driver looks
> worth investigation too -- its design is rather more reassuring
> than lvm2 snap.

Perhaps it is better to have the writable/client-specific parts of your 
root filesystem (/tmp, /var/tmp, perhaps /etc) mounted via NFS (or 
something else, or just as symlinks to a separate device) on top of a 
read-only generalized rootfs (like the debian diskless packages used to 
do), rather than trying to handle this at the block-level. It seems to 
me all sorts of bad stuff can happen with a writable block-level 
overlay, for instance if you try to upgrade the filesystem underneath.

Jacob


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