>> Just image the scenario where you need to restore a critical file with
you CEO watching and have to explain that it is going to take an hour
because there are 5 tape mounts involved and each has to seek across 75GB of
tape surface.
That's another reason I'm considering STAC Replica NDM
(http://www.stac.com/cw/) for desktops and mobile PCs. No tapes!!! What do
you think?
Regards,
Orin Rehorst
-----Original Message-----
From: Garin Walsh [mailto:Garin_Walsh AT NOTES.SABRE DOT COM]
Sent: Monday, November 29, 1999 11:50 AM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: Tape Library Recommendation
Orin,
Two things that bit me when planning my current install are
that I
underestimated tape usage and the number of drives needed.
1. Unless you run reclaims all the time (see 2. for the
downside of this), your
tapes will average about 40% occupancy regardless of
collocation usage or not.
On day one you get 100% occ. but over time the reclaimable
percentage goes up
reducing the effective storage of your library. So, once you
figure out the
number of files you will store and your retention times and
whatnot then
multiply that by two to account for the "not yet reclaimed"
space on tape. Just
an opinion here but if I had done the x2 I would have met my
planned need -
thankfully we have not met our growth plans.....
2.Get at least 3 drives in a library. If you have physical
limits on your disk
pools, database, log, or tape pools and/or more than
intermittent restores or
use HSM then you will start having contention between
reclamation, database
backups, storage pool backups, and restores. ADSM has a
priority scheme for this
through canceling and schedule order but it is frustrating
to have processes
wait for tape drives. If you look at the DLT drives some of
those mount/seek
waits can be quite long. If you have many clients and a
"small" disk pool you
can get a scenario going where every client will want to put
at least one file
directly to tape before writing to disk pool. For instance,
on a library with
two drives, if you have a reclaim running and client backups
start, they will
write to the disk pool. At some point migration will kick
off for the disk pool
which will wait for the reclaim to finish. When the disk
pool fills all the
pending clients will go into a media wait status. Now
everything waits for the
reclaim to finish. When it does, the migration for the disk
pool will start - if
you run two migration processes the clients will still wait.
When the migration
is done and at least one drive is free, one of the clients
will allocate that
drive and start writing its next file to it. Even though
there is free space in
the disk pool all the media wait clients will still wait for
a tape drive. Each
individual client will mount a tape to dump a file to it
before going back to
writing to the disk pool. If you are using a high capacity
tape these mounts and
dismounts can be expensive time wise and all the time these
tapes are mounting
and dismounting the disk pool is filling again and so it can
all happen again.
And again. Worst case you could wind up with a tape mount
per file. Ick.
From an opinion standpoint, restores should drive your
decision process for
media and tape size. Bigger is not better in some cases.
Just image the scenario
where you need to restore a critical file with you CEO
watching and have to
explain that it is going to take an hour because there are 5
tape mounts
involved and each has to seek across 75GB of tape surface.
If you had the money,
you might want to consider two libraries, large capacity DLT
tape for the
storage pool and something with faster access, Magstar for
instance, for the
primary backup pool - just a thought.
Oh, and try to take a class. ADSM is a different beast from
rest and in the good
old IBM tradition there is a lot of up-front knowledge
necessary to set things
up correctly. Makes future management much easier. The
Redbooks are also
helpful.
Garin Walsh
Sabre Inc.
"Robinson, Cris" <Cris.Robinson AT LIBERTYMUTUAL DOT COM> on
11/29/99 11:39:59 AM
Please respond to "ADSM: Dist Stor Manager"
<ADSM-L AT VM.MARIST DOT EDU>
To: ADSM-L AT VM.MARIST DOT EDU
cc: (bcc: Garin Walsh)
Subject: Re: Tape Library Recommendation
Orin...
There are other considerations also. How many inactive
versions of files do
you plan to keep? How many deleted version do
you plan to keep. Also, how long do you plan to keep
inactive and deleted
copies? Are you archiving at all with ADSM?
Are you planning to do any disaster recovery i.e. off site
tape vaulting? It
could make a difference.
I would go DLT from personal exerience. Cost per tape is
~$80 depending on
vendor with 4000 drives you get 40GB, 20 Compressed.
7000's get 70GB and 35 compressed.
For administrative and growth purposes I would go with a
Library over a
changer.
StorageTek has the 9730 which can hold up to 28 tapes with 4
DLT drives or
30 tapes with 3 drives.
ATL has a similiar system called the P1000.
DLT 4000 drives for these units run about $5000 or so
DLT 7000 drives run about $10000 ( they hold more data per
tape )
DLT 4000's should be fine. I would think anyway.
And you thought you were asking a simple question!
C
__________________________________________________
Cris Robinson
Sr. Technical Analyst
Enterprise Storage Management / TSM (ADSM)
Liberty Mutual Insurance
Portsmouth, New Hampshire
603.431.8400.54837
mailto:cris.robinson AT libertymutual DOT com
-----Original Message-----
From: Orin Rehorst [SMTP:rehorst AT POHA DOT COM]
Sent: Monday, November 29, 1999 10:25 AM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Tape Library Recommendation
* What do you recommend for an entry level
library on a
limited >
budget?
*
* I'm > backing up 8 servers and about 15
users. Could go
conceivably
up to 10 > servers and 100 users. Max storage of
about 250 GB.
>
> A single tape drive and a small one-drive
library?
>
> A small library with two drives?
>
> DLT?
>
> What brand and model(s)?
>
> TIA
Orin Rehorst
Port of Houston Authority
(Largest U.S. Port in foreign tonnage)
e-mail: rehorst AT poha DOT com <mailto:rehorst AT
poha DOT com>
Phone: (713)670-2443
Fax: (713)670-2457
TOPAS web site: www.homestead.com/topas/topas.html
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