Hello Richard!
I understand your arguments are "either veracity or performance".
I believe the point you possibly oversee is that
if db reads were made from both sides of the mirror
then db backup performance would (with high probabilty) significantly rise
without harming database veracity.
However, this is theory only, as this is apparently not implemented in TSM DB,
point.
Consequently both your and Orville´s conclusions are correct.
Combining reliability and speed in current designs would lead to
implementig both HW mirroring and TSM mirroring, at extra costs$.
best regards
Juraj
> -----Ursprüngliche Nachricht-----
> Von: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] Im
> Auftrag von Orville Lantto
> Gesendet: Mittwoch, 25. April 2007 21:22
> An: ADSM-L AT VM.MARIST DOT EDU
> Betreff: Re: TSM only reads from COPY1 during DB backup
>
> Performance is the issue. As tapes get faster and faster,
> trying to get a db backup without "shoe-shining" the tape
> drive gets harder. Using storage sub-system mirroring is an
> option, but not the recommended one for TSM. Perhaps there
> is a sound technical reason that db reads cannot be made from
> both sides of the mirror, but it could be that it was just
> programmer "convenience". Either way, I will have to design
> around this "feature" to squeeze a bit more performance out
> of my storage.
>
> Orville L. Lantto
> Glasshouse Technologies, Inc.
>
>
> ________________________________
>
> From: ADSM: Dist Stor Manager on behalf of Richard Sims
> Sent: Wed 4/25/2007 10:49
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: Re: [ADSM-L] TSM only reads from COPY1 during DB backup
>
>
>
> On Apr 25, 2007, at 10:55 AM, Orville Lantto wrote:
>
> > Reads should be safe from mirrored volumes and are commonly done in
> > operating systems to load balance. Not taking advantage of the
> > available IO resource is wasteful and puts an unnecessarily
> unbalanced
> > load on an already IO stressed system. It slows down db
> backups too.
>
> Then your issue is performance, rather than database voracity.
> This is addressed by the disk architecturing chosen for the
> TSM database, where raw logical volumes and RAID on top of
> high performance disks accomplishes that. Complementary
> volume striping largely addresses TSM's symmetrical mirror
> writing and singular reading. Whereas TSM's mirroring is an
> integrity measure rather then performance measure, you won't
> get full equivalence from that.
> Another approach, as seen in various customer postings, is to
> employ disk subsystem mirroring rather than TSM's application
> mirroring. In that way you get full duality, but sacrifice
> the protections and recoverability which TSM offers.
>
> Richard Sims
>
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