Somewhat, but not entirely, if you are using real tape.  (If you are using
virtual tape, it just doesn't matter.)

Day 1:  When you use subfile backup, you get a base copy of the entire file
the first backup.
Day 3:  The next backup of that file just backs up the changed blocks/bytes.
Day 4-26:  No changes to the file, no backups
Day 27:The next backup of that file just backs up the changed blocks/bytes.

etc.
Until a point the client decides it's more efficient to back up the whole
file again rather than doing another subfile.

Without collocation, restoring that file will likely require 3 tape mounts.

With collocation on, TSM will TRY, but cannot guarantee, that backups for
client XXX go on the same tape.  And at some point, due to other data that
gets backed up from the client, that tape will fill and spill over into a
second tape.  So it just depends.

If you had to a restore on Day 4, there is a good likelihood that you could
rebuild/restore the file with 1 tape mount.  If you do a restore on Day 28,
who knows, may take 2.

But also remember, extremely tiny files and files over 2 GB are not
processed by subfile backups.

And it depends on what your usual restore activity and service requirements
are.  If your customers are calling you every day for restores, they may
notice the extra mounts and complain.  If they are calling for 1 restore a
month, nobody will care.

W




On Wed, Jan 21, 2009 at 9:52 AM, Kinder, Kevin P <Kevin.P.Kinder AT wv DOT 
gov>wrote:

> I haven't used the following two features in combination yet, so a
> question:
>
> If I were backing up using subfile and collocation, would this alleviate
> the problem of the subfile backups being spread over many volumes?
>
> ----------------
> Kevin
>
> -----Original Message-----
> From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf 
> Of
> Jason Clarke
> Sent: Tuesday, January 20, 2009 7:16 PM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: Re: [ADSM-L] Unexpected behavior - Win2k3, TSM 5.4, NTFS
> permissions
>
> Hi Mark,
>
> Thanks for your comments. I've decided to not go with subfile backups
> because (from training late last year) I understood that a 1MB file
> could be backed up over many volumes, thus being insanely slow to
> restore.
>
> The spike of 120GB isn't a huge problem. Currently, we're only have
> about 2TB of data that needs backing up. We've installed a IBM TS3200
> (44 slots) with 2x LTO3 drives. Along with a 500GB disk pool that
> clients spools to first. At 3 backup revisions of most of the data, we
> should have room for expansion.
>
> However, on thinking about that 500GB, I'll probably up it as one of our
> servers is expected to grow beyond that in size.
>
> Thanks again for the comments.
>
> Cheers,
>
> Jason
>
> -----Original Message-----
> From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf 
> Of
> Mark Stapleton
> Sent: Wednesday, 21 January 2009 10:51 AM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: Re: [ADSM-L] Unexpected behavior - Win2k3, TSM 5.4, NTFS
> permissions
>
> From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf 
> Of
> Jason Clarke
> Last night, the client backed up 129GB, which is about 125GB more than
> normal.
>
> On any given day, during the holidays, theres about 2-3GB of changed
> files.
>
> However, I did change a permission on a directory/folder tree that
> contains 125GB of files.
>
> I'm guessing TSM has backed up the whole file because of the permission
> change. I'm guessing this is because subfile backup isn't being used
> here. If subfile was turned on for that client, would it reduce the
> amount of data it decided to backup?
>
> Yes, subfile backups would decrease the amount of data you would have
> backed up. However, you will eventually have to back up the entire set
> of files eventually, because subfile backups allow a limited number of
> deltas to be backed up, and will only affect files greater than 10kB and
> less than 2gB. Also keep in mind that if you have, say, 100,000 files,
> and you have 5 deltas for each file, you're going to have to make
> restore 600,000 locations on tape--1 for the last full backup of a given
> file, and 5 for its subsequent deltas. Subfile restores are very, very
> slow, and are more designed to accommodate backups across slow (i.e.,
> T-1) bandwidth pipes.
>
> TSM treats files as whole entities. When you change permissions on a
> file, TSM will back it up again. Might I suggest that you stage such
> mass changes so that you don't get hit with such a spike again?
>
> --
> Mark Stapleton
> System engineer, CDW
>
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> 1/19/2009 8:52 PM
>
>