06-08-06 06:14 PM
Gary,
The answer is: it depends. And, until you determine some of the
following it's not going to be easy to predict.
1) Are you collocating or not?
2) Are you using tape hardware compression or compression at the node?
What is the compression %? Do not use both. If you are backing up
systems located in the same facility as the TSM server, don't compress
on the node; let the tape hardware do the compression. If you are
bandwidth constrained, compress on the node, but not on the server. If
you are bandwidth constrained and you are not a 24x7 shop, try running
the backup uncompressed at the node (you will take an initial hit the
node backs up the first time, but it should be fine thereafter
depending on the volume of data). If you are bandwidth constrained run
uncompressed, but have the network guys put ACL's on the router to
change the bandwidth available for TSM backups during peak hours.
Running compression on the node is really resource intensive and will
cause performance degradation.
3) How much data are you going to backup to system?
#1, #2, and #3 will determine the base number of tapes.
Once you get the base number of tape, you need to add tapes based on
the following . . .
4) What is the % changed files in your nightly backup; remember that by
default TSM only backs up changed files? This is easily calculated by
find the %ratio of total nightly backup to total data on all nodes then
multiplying by verexists. From this subtract the amount of data
deleted (continuing to account for the two verdeleted for 31 days and
an additional 29 days for the retonly copy).
5) How often are you running expiration?
This rate of change and the expiration will determine the how fast
tapes will come back from the copypool (I assume you are using Disaster
Recovery Manager). This is a simplistic approach to getting to an
answer. All these factors will play a part in determining the number
of tapes for all pools.
Remember . . .
If a file is backed up by TSM and it stop changing and is never
deleted, the active copy can be retrieved from the TSM server forever.
If the file changes, the different versions will be kept for a
combination of verexists and retextra days based on how frequently the
file changes. For example, if a file is created today, backed up by
TSM today, and then the file never changes: only one copy of the file
is stored on TSM; not the number specified by verexists. Verexists
will only come into play if the file changes and continues to change.
Another factors: how often are you running reclamations? How many DB
backups are you keeping? What is you reuse delay set to?
Also, the management class is applied to node data wherever it is
stored. If you have data from a node that is bound to this management
class stored across all four pools, the variables apply to that data in
each pool. The variables do not get applied to the pool; rather to the
data in the pool.
Lastly and I am just wondering about this: do you really need
28-versions of a changing file? Remember, the current active version
of the file is available for restore forever. If the file stops
changing but continues to live on the node, you can still restore your
active version forever and the inactives for retextra days. If the
file is deleted, you will have the last two versions available for
31-days (retextra) and the latest version for an additional 29-days
(retonly). Of course, if you require the 28-versions, this impacts DRM
and thus the number of tapes.
Hope this helps.
Mahesh
gary.matthews@logicacmg.com wrote:
> Hi,
>
> Am a complete newbie when it comes to TSM and have just been handed a
> W2K3 system to look after with TSM 5.3. The system hasn't gone live yet
> and I'm trying to work out how many tapes I'm going to need for
> offsiting. We have four pools for onsite with the following setup
>
>
> Vers Data exits 28
> Retain extra(days) 31
> Vers Deleted 2
> Retain Vers (days) 60
>
> Do the copypools have the same characteristics? If I'm sending four
> tapes off a day how may tapes do I need for an offsite cycle ?? It's
> just that the company that set things up have said that 30 LTO-3s
> should be enough for onsite and offsite and I can't see how.
>
> TIA
>
> Gary (confused!)
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