Re: LTO4 vs LTO3 speed

Paul,

How long ago did you move to the saving SAVFs?

Reason I ask, I worked on a system that originally did that. But after a
couple of upgrades, it was faster to save directly to tape.

Its a smaller box, so it only has 8 disks. So the limiting factor isn't
really the tape, it's the disks. Reading and writing to the same set was
slower than streaming to the tape directly.

Charles


On Fri, Jun 14, 2013 at 5:11 PM, Musselman, Paul <
pmusselman@xxxxxxxxxxxxxxxx> wrote:

Have you looked at what kinds of things you're saving? Lots of little
things take more time to write to tape than a few big things!

We needed to structure our backups more efficiently, so we changed saves
of some of the system stuff-- outqs, journals, configuration, history logs,
security data, etc. to use SAVFs in a "SAVF Library." We then saved the
library to tape. The save was much quicker. "Much" is purely subjective--
I don't have hard numbers-- but the difference was noticeable. Instead of
several hundred individual QHST files, it's 1 SAVF.

Our main goal was more efficient use of our tape drives. Saving to SAVFs
took jobs that ran "quite a while" collecting data, and a little time
writing to tape, and moved the 'collecting' to 4AM, while the writing was
still with our evening backups. The write of the library to tape takes
about 10 minutes, while the individual saves can each take 10 minutes.
We're trading disk space for tape time.

Another piece of anecdotal data-- the contract on our tape library was up
for renewal, and we were considering moving from LTO-4 to LTO-5. The
difference in speed wasn't that impressive; the capacity was nice, but not
Earth-shattering. And if we continued to use our vast collection of LTO-4
tapes, we wouldn't see any of the increase in speed or capacity. Since our
daily backups fit on LTO-4 tapes with LOTS of room to spare, we kept the
LTO-4 drives. They are 'fast enough.'

Paul E Musselman
PaulMmn@xxxxxxxxxxxxxxxxxxxx

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