ADSM-L

Re: [ADSM-L] Backing up Light Speed compressed files

2010-04-28 18:26:24
Subject: Re: [ADSM-L] Backing up Light Speed compressed files
From: "Huebner,Andy,FORT WORTH,IT" <Andy.Huebner AT ALCONLABS DOT COM>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Wed, 28 Apr 2010 17:25:05 -0500
LTO2 writes to tape at maximum of 40MB/sec.  If the data compresses 3.5:1 then 
your server will need to feed the tape drive at 140MB/sec to keep up with the 
write speed.  If the data compresses 1:1 then you only need to send data at 
40MB/sec.
This kind of thing used to drive me nuts until I figured out it takes about 1 
hour to fill one of my tapes, regardless of the amount of data written.  If it 
takes longer then there is a problem.  In your case 85 minutes is the minimum, 
probably a little under 2 hours is a realistic time.


Andy Huebner

"You have to think 4th dimensionally."
                                        Emmitt L. Brown


-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of 
David Longo
Sent: Tuesday, April 27, 2010 1:44 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: [ADSM-L] Backing up Light Speed compressed files

I have never been concerned with compressed files, never used
 compression on TSM - except on my  LTO tapes.

Now, we have a new situation. We have had a client with SQL DB and
the DBA's do the dumps to disk and I pick up.  (Can't use TDP SQL,
long story.)  The dumps were lately (6) 200 GB files, total 1.2 TB and
growing daily.  Took about 11 hours to backup directly to LTO2 tapes.

DBA's just implemented using Quest's Light Speed using their Level 4
compression - whatever that is.  The dumps are now (4) 62 GB files,
so about a 5 to 1 compression.

The TSM backup took much less time, but not as much less as expected.
When the offsite copy was made, LTO2 to LTO2, I found out why.
For a certain file size, it takes twice as long to back it up for a
compressed file as an uncompressed file.

For more info, on the LTO2 tapes, before we would get just over 700 GB
on them, now just over 200 GB.  (Using q vol stats).  I kinew it would be
less obviously.

Anybody know why takes twice as long?  Is there a way to speed it up?

Thanks,
David Longo



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