We created tapes equal to storage and we usually run about 10-15%
utilized on disk space. The daring people might be able to go 10% over
safely, but we are a little paranoid and have chosen to not over commit.
Andy Huebner
-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
wanda.prather
Sent: Thursday, June 21, 2007 2:35 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: [ADSM-L] FW: Somewhat OT: Sizing a VTL solution
I agree! That's the method I would use.
TSM thinks the VTL is a tape library, and processes it as such.
So you need to look at how many volumes you are using, not just how much
space.
If the numbers you see for volume usage don't square with your
occupancy,
better find out why!
In most customers, I find their overall tape utilization is at best
around
65% full (because there are tapes in FILLING status, DB backup tapes,
EXPORT
tapes, scratch tapes, tapes that are below the reclaim threshold, etc.)
And as far as I can tell, if you set your reclaim threshold to 50%, over
time you can, quite by accident, end up with hundreds of tapes sitting
at
49% that never reclaim without manual intervention. You can be more
aggressive about running reclaims in a VTL. But you still have to
account
for un-reclaimed tapes and volumes that never fill (like DB backups).
Now I know some VTL's will allocate their physical storage in chunks
(say 5G
for example) as a tape is written/appended to. So if your virtual
volumes
are 100G, but your DB backup only needs 20G, you will only be using 20G
of
the backstore. But if your DB backup needs 21G, you will be using 25G
of
the backstore. SO it is possible to get away with creating more virtual
volumes than you actually have space to support. But I'm very leery of
attempting to overcommit volumes in the VTL, given that TSM tries its
best
to create full volumes.
What I would like to know is if anyone has good ideas on what level of
overcomittment you can get away with? Or is it better just not to go
there?
W
_____
From: ADSM: Dist Stor Manager on behalf of Andy Huebner
Sent: Thu 6/21/2007 2:21 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: Somewhat OT: Sizing a VTL solution
The approach I used worked very well. I counted all of the tapes that
would
be kept on the VTL and multiplied that by the capacity of the tapes. I
then
calculated the growth rate of the tape pool and added that to the total,
in
my case 6 months out. That is the number I used.
The assumption is that compression will be similar on both.
If you calculate off of occupancy there is a greater uncertainty because
you
do not really know how much compression you will get. Calculating off
of
tape counts will be inaccurate because of filling tapes, but this error
is
in the admins favor. Filling tapes can be factored in to reduce the
error.
Andy Huebner
-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
William Boyer
Sent: Thursday, June 21, 2007 1:03 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: [ADSM-L] Somewhat OT: Sizing a VTL solution
Has anyone just gone through sizing a VTL solution for a library
replacement? Is it as simple as taking your current occupancy/retention,
applying for some compression and using that figure for the amount of
storage behind the VTL? Or maybe I'm just trying to make something
harder
than it is. Wouldn't be the first time!
:-)
TIA.
Bill Boyer
>Select * from USERS where CLUE>0
0 rows returned
This e-mail (including any attachments) is confidential and may be
legally
privileged. If you are not an intended recipient or an authorized
representative of an intended recipient, you are prohibited from using,
copying or distributing the information in this e-mail or its
attachments.
If you have received this e-mail in error, please notify the sender
immediately by return e-mail and delete all copies of this message and
any
attachments.
Thank you.
This e-mail (including any attachments) is confidential and may be legally
privileged. If you are not an intended recipient or an authorized
representative of an intended recipient, you are prohibited from using, copying
or distributing the information in this e-mail or its attachments. If you have
received this e-mail in error, please notify the sender immediately by return
e-mail and delete all copies of this message and any attachments.
Thank you.
|
