[ale] Sportin' SCSI/RAID

[Jeff Hubbs]

Eric -

My only real clustering experience is under VMS, in which case the systems do all
mount the same volumes and in some cases do it over a SCSI channel.  The DEC
AlphaServers I worked with most recently had outboard RAID controllers and shared a
set of disks between them, cut up into several RAID arrays.  I'm not trying to
contradict you, though - I have every expectation that there was some mechanism that
made one controller or the other "lay out" while one worked the drives.  At the time
I got laid off, we were working on an Ultra-SCSI-2 SAN connecting three nodes.  But,
yes, it's looking like in Linux at least, what I'm
finding is that there's not a similar mechanism, at least not yet.

Actually, I was not looking at this in terms of a cluster per se - I was trying to
work out a possible arrangement of machines for a public/private Internet Web server
in which one machine ran Apache and MySQL (but only reading a database) and the other
ran Apache and MySQL (read/write).

- jeff


"Eric Z. Ayers" wrote:

> Hello Jeff,
>
> Most UNIX clustering solutions don't allow both machines to mount the
> same SCSI target,LUN at the same time.  In fact, the SCSI protocol has
> this concept called a reservation which explicitly prohibits two host
> adapters from talking to the same device simultaneously.
>
> -Eric.
>
> Jeff Hubbs writes:
>  > Does anyone here have any experience with sharing a RAID array between two
>  > Linux systems over a common SCSI bus?  What is required?  What are the
>  > gotchas?  Is it less of a problem if one of the two machines only reads from
>  > the RAID volume?
>  >
>  > If the shared RAID array in question held, say, a MySQL database, how would
>  > both machines access it (again, presuming one machine only reads)?  An
>  > instance of MySQL on each system?
>  >
>  > - Jeff
>  >
>  > ** Happy Holidays to the ALE! **
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