Re: LTO to LTO2 - restore times

The most favorite answer in the industry - it depends!
In theory you should get up to 33% performance boost: LTO1 drives have
native speed of 15 MB/s, while LTO2 drive accessing LTO1 media should give
you 20 MB/s. Compression multiplies these numbers accordingly.
In real life you can get the bottleneck moving from tape to something else
as part of the change.

Example
Assuming 2:1 compression
Assuming disk array read rate 35 MB/s and write rate 25 MB/s
Former tape write rate 30 MB/s (15 MB/s native), the tape is the
bottleneck and limits backups to 30 MB/s
Former tape read rate 30 MB/s (15 MB/s native), the disk is the bottleneck
and limits restores to 25 MB/s
Upgrade of LTO1 to LTO2 drives using same LTO1 media will produce:
New tape write rate 40 MB/s (20 MB/s native), now the disk becomes the
bottleneck and limits backups to 35 MB/s. Speed improvement of only 16,7%
New tape read rate 40 MB/s (20 MB/s native), the disk is still the
bottleneck and again limits restores to 25 MB/s. 0% improvement.

If you add processors, I/O busses, SCSI/FC HBAs or SAN to the equation,
the things are harder to calculate but in general you are having more
chances to hit another (hidden) bottleneck! As with all upgrades.

Zlatko Krastev
IT Consultant






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16.09.2003 13:48
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        Subject:        LTO to LTO2 - restore times


All

Just wondered if anyone has upgraded from LTO to LTO2, and what difference
this made if any, to restore times and stgpool backup times.

Regards

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