Jack,
>> "Before someone crys foul, yes you can use TSM to backup directly to
tape, especially for large files, but I havn't heard of people using
this much, and it is an issue if you need to keep the tapes streaming
and there isn't enough bandwidth"
Depends on how you're feeding those hungry tapes, and what kind of tape
hardware you're using.
Backing up our Oracle databases over the SAN (using RMAN/TDPO) is
*ideal* for streaming directly to tape, and we have seen speeds of up to
40MB/s per channel. As far as tape hardware is concerned, it depends if
your tape device streams at a fixed rate - LTO gen 1 drives did this,
but were much improved by the LTO gen 2 drives which step their speed
according to how fast the data is streaming in to it, thus in theory
reducing the dreaded back-hitch.
Rgds,
David McClelland
Tivoli Storage Manager Certified Consultant
Management Systems Capabilities Group
Shared Infrastructure Development
Reuters
85 Fleet Street
London EC4P 4AJ
E-mail david.mcclelland AT reuters DOT com
Reuters Messaging david.mcclelland.reuters.com AT reuters DOT net
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-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Coats, Jack
Sent: 19 July 2004 18:26
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: Multiplexing to a single tape
My info is old, but my guess it hasn't changed much since I used to work
for a VAR and we sold both TSM and Veritas NetBackup:
Veritas multiplexes blocks from various backup clients on the tapes when
this is being done. It works, and is very effective. They basically
used a hacked version of gzip to prepend the node name/sequesnce number
(effectively) on the data block before it is written to tape.
This is best used when writing directly to tape from multiple clients
backing up at the same time. If you keep the tape fed and you have
enough bandwidth, you can keep the tape streaming. For performance you
MUST keep the tapes streaming. (I think I heard that you may be able to
backup to disk now, and then backup to tape, but I never used it, and I
may be mis-remembering too.)
Scaling backups with Veritas has to do with bandwidth, tape streaming
speed, number of concurrent clients you are backing up, and number of
tape drives available to backup to.
TSM does this as a two step process. Backup to disk local on the TSM
machine, then put the files from disk to tape. This does not
'multiplex' like Veritas does, but it intermingles files from various
clients on the same tapes. Since the disk drives are local, and if your
TSM server is configured correctly (I have one with a problem, so ...)
you can keep the tapes streaming by sucking the data from disk. (Before
someone crys foul, yes you can use TSM to backup directly to tape,
especially for large files, but I havn't heard of people using this
much, and it is an issue if you need to keep the tapes streaming and
there isn't enough bandwidth).
This means that Veritas requires less disk and better bandwidth from
clients when backups are happening, and TSM can handle small clients,
random backup times, and low bandwith situations much better than
Veritas. But TSM does require the disk space, and a good database.
Veritas has the benefit of if the database 'catalog' is destroyed and
you cannot get the catalog back from a backup, you can re-bulid the
catalog, but you have to spin all the tapes, end to end. (Veritas seems
to be an easier 'sell' because it is full+diff/incremental type of
backup rather than TSMs 'incremental forever'. After 3years management
here still doesn't have that
down!)
TSM and Veritas have the SAME problem when it comes to restores. They
both MAY have to spin a number of tapes to perform one (non-trivial)
restore.
In general, TSM uses more disk, Veritas uses more tape drives, TSM must
have some 'downtime' for reclaimation. Database maintenance on both
systems is needed to keep things optimal.
I hope this helps ... Jack
-----Original Message-----
From: Gill, Geoffrey L. [mailto:GEOFFREY.L.GILL AT SAIC DOT COM]
Sent: Monday, July 19, 2004 11:06 AM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Multiplexing to a single tape
I was wondering if anyone was multiplexing backups to a single tape.
Recently I attended a Veritas class, our "other" new backup system, (yes
I did ask to stay completely with TSM) and they really touted this as
what seemed like a very good means of backup. Unless you have the newer
faster technology tape drives I'm not sure I agree with it but don't
have experience since disk pools have always been plentiful. I'm not
sure I agree with it anyway because I believe restores would be slow
since data would be scattered throughout the tape. What if multiple
restores need the same tape? Can they run at the same time and if so
wouldn't that be even worse?
So the question I have is, has anyone tried this functionality with TSM,
or Veritas for that matter since I believe there are others on the list
that use it. I am interested in any feedback so feel free to praise or
rail on it.
Thanks,
Geoff Gill
TSM Administrator
NT Systems Support Engineer
SAIC
E-Mail: gillg AT saic DOT com
Phone: (858) 826-4062
Pager: (877) 854-0975
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