iscsi and geom mirror - stupid idea or not ?

[pete wright]

On 4/19/07, Pete French <petefrench at ticketswitch.com> wrote:
> what would happen if I made a machine which contained a mirrored
> geom pair consiting of one local driive and one drive accessed via iscsi on
> a remote machine ? would this work ?
>
> what I am considering is two such machines, geographicly distinct. one is
> a 'master' and boots off the mirrored drive, the other is a slave and
> has a separate boot drive which just rngs FreeBSD to make the drive inside
> it into an iscsi target for the first machine. The idea here is if the first
> machine is catastrphicly killed (like building falls down on it or
> something) then the second one can be rebooted from the internal drive, and
> will hence become the first one. It's basically a way of making a standby
> machine in case of disaster.
>
> I havent really looked at iSCSI until recently, and this is just one of
> the ideas I came up with looking at the possibilities.
>

iSCSI is good for many things - although i would not suggest this
setup.  it sounds like you are trying to use the mirror/iSCSI
architecture as some sort of backup scheme.  it may make more sense to
capture snapshot's of your data and mirror that off to secondary
storage.

along these same lines is a common iSCSI implementation of having a
dedicated piece of hardware that manages RAID, grouping of LUN's and
other management functions.  this allows you physically, and
logically, implement some sort of redundancy/backup schema independent
of the iSCSI consumer (i.e. the OS that will be mounting the iSCSI
volume).  let the machine hosting the iSCSI storage do it's job, and
let the client do it's job - it does not make sense to try to mix
these too.

so the short answer is i would not try to mix iSCSI volumes with local
volumes via a software mirror.  a properly implemented iSCSI solution
can easily account for DR situations, and using filesystem
snapshotting will make this task easier as well.

-pete



-- 
~~o0OO0o~~
Pete Wright
www.nycbug.org
NYC's *BSD User Group