I'd heard this before too and have been following this advice. We use
Roadrunner with software compression and have hardware compressions turned
off.
David Knispel
[log in to unmask]
Phone: 513-248-5029
Fax: 513-248-2672
----- Original Message -----
From: Arthur Frank <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, March 31, 2000 3:09 PM
Subject: Re: compression vs no compression, was New DDS-3 drive ,speed vs D
DS-1
Lee,
You're using a mix of hardware AND software compression? I thought I heard
from somewhere (I don't remember where) that this wasn't a good idea.
"Either hardware, or software, but not both."
Has anyone else heard this? Have I been misinformed?
Art Frank
Manager of Information Systems
OHS Foundation
[log in to unmask]
(503) 220-8320
>>> Lee Gunter <[log in to unmask]> 03/31 11:21 AM >>>
We implemented Orbit's DLT4000 solution very early on, and we were advised
by
Orbit, then and now, to not enable full software compression in backups to
these
devices because the data could become unreadable on restore. We currently
use a
mix of drive compression and level 1 (2:1) software compression. In our
last
full system backup, we stored 268.4 GB in 7.5 hours to four drives in
parallel,
which translates to 2.45 MB/sec/drive -- a bit less than the 3+ MB/sec I
would
expect w/ this level of compression. Also, we must keep our drives
configured
as DDS-2 drives due to shortcomings in HP's DLT4000 software driver, and
this
prevents us from disabling hardware compression - the drives don't respond
to
this directive while configured as DDS-2's (C1521B). I don't believe that
this
has changed, and I don't particularly like not being able to use the native
drive type. This was originally necessary due to a lack of fast search (and
other?) capability in the DLT4000 driver, which has since been fixed, AFAIK.
Orbit still advises using the other device type, however.
When we used two 7980XC drives, we could enable full software compression
and
disable drive compression. This resulted in near full streaming throughput
and
fully utilized the CPU -- but we also used 90-100 tape reels in the process.
Our first implementation of the DLT solution with three drives in parallel
cut
the backup time nearly in half, but we're now back up to where we were a few
years ago. We're looking at their online module, now -- I'm just a bit
nervous
about it's support of our user logging environment (w/rollback recovery
enabled
on the databases).
----
Lee Gunter The Regence Group
Supervisor, TRG HP/MPE Systems 503.375.4498
----
Opinions expressed are solely mine.
From: Chris Goodey <[log in to unmask]> on 03/31/2000 10:39 AM
Please respond to Chris Goodey <[log in to unmask]>
To: [log in to unmask]
cc: (bcc: Lee Gunter/BCBSO/TBG)
Subject: Re: [HP3000-L] compression vs no compression, was New DDS-3 drive,
speed vs D DS-1
Now that we know a DDS-3 drive is maybe 5 times faster than a DDS-1 drive
when used WITHOUT compression, the next question is: Why not use
compression?
A recent TurboStore timing I did storing to a DDS-2 drive, with hardware
compression,
reported about 1.4 megabytes a second actual through-put (those data bases
compress well,
especially since they are seldom filled to capacity.)
Now I suppose if you have a very fast cpu it might be able to compress
better
than the tape drive, in which case you would want to turn off hardware
compression.
But in general, are we not better off just leaving compression on in
hardware?
(yes, if writing a DDS-1 tape it would be better for compatibility with old
drives
not to compress, but this is a special case.)
Has any done any testing of hardware versus software compression with
TurboStore and Orbit
backup? My guess was that at the highest compression level, the software
might be better,
but it is enough better to worry about?
> -----Original Message-----
> From: Bruce Toback [mailto:[log in to unmask]]
> Sent: Friday, March 31, 2000 10:01 AM
> To: [log in to unmask]
> Subject: Re: New DDS-3 drive
>
>
> Art Frank asks:
>
> >2. How much faster (roughly) is [DDS-3] than the C1503 DDS-1 drive
> >that it is replacing? Hardware compression is off.
>
> DDS-1 native transfer rate to tape is 173 KB/s. DDS-3 native transfer
> rate to tape (using DDS-3 media) is 1 MB/s. The channel may be slower
> than that.
>
> -- Bruce
>
> --------------------------------------------------------------
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