Re: DLT Backup/Restore Speed
From: Mike Brown (mike_at_tkg.ca)
Date: 12/31/04
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Date: Fri, 31 Dec 2004 13:06:41 -0500
JP wrote:
>
> > The speeds you are seeing are normal, depending on the drive and
> > compressability
> > of the data. Using the HP DLT VS80 on a ML530 I see a 38.76 Gbyte backup
> > in
> > 3:43:55, or about 180.17 MB/min. The VS80 version is rated at 3MB/sec to
> > the
> > tape, or about 6MB/sec with 2:1 compression overall. Some of the DLT
> > drive
> > run at double this speed, check the specs on yours.
>
> I am using VS80 on an Adaptec AD160 SCSI controller. No other devices are
> connected to the same controller. Hard drives are all 15,000rpm. When I
> checked the BackupEdge reports, no compression was used during the backup
>
I would doubt if SCSI or controller sharing would have an effect on the
throughput of the VS80. Even a rate of 10 Mbytes/sec is fast enough,
and you are likely set at 20 with that combination.
> > If I assume 1/2 the time for a backup, you have a throughput rate of
> > around
> > 6MB/sec to the tape drive. What does the Edge summary file say?
> BackupEdge reported a throughput of 236.9Mb/min, which is within the range
> you mentioned. The time it takes to backup is acceptable. Since I use
> byte-by-byte verification, it occupies 2/3 of the time of the entire
> backup/verification process.
>
> What I still don't understand is why it always takes 2 hours to restore a
> files, even though it is just as small as 100Kb.
>
You need to use FFR, what is happening is your are reading the whole tape
to find the file. It may be that even if the file is half way through,
Edge has go to the end in case there is another match on your pattern.
With FFR the tape is indexed during the verify stage, and a database
file is stored on the HD. When you want to recover a file, Edge checks
the database file, calculates about how far along the tape the file is,
the fast forwards to that area. Edge then starts reading the tape and
restores the file(s). In many cases the file restore can happen in as
little as 90 seconds for smaller files. I use it all the time.
> > Your best bet for overall speed is to upgrade to the current version of
> > BackupEdge,
> > 02.00.03. Configure it for software compression ( which will turn off the
> > drives
> > compression ) and play with the tape block size, try 128 first.
> It is hard to justify the upgrade if I cannot tell for sure that it will
> improve the speed. But I can try changing the block size first.
>
You can download and try the newer version before buying it. Make sure
to save your info and register files under the config subdirectory of
your current version so you can relicense it.
The zlib based compression in the new version allows for better compression
ratios then what is in the tape drive, and generally faster backup and restore.
I think the upgrade cost is very nominal, maybe $150 USD.
> > Are you indexing the backup and using Microlites FFR?
> No. I have been using the very basic features.
>
You need to scan through the manual on indexing and FFR.
> Thanks, Mike.
>
> Cheers,
>
> Joe
Mike
-- Michael Brown
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