My thanks to Jeff Kennedy, Dave High and Larry Kingery for being very
quick off the blocks. They've convinced me to go for it. To summarise
/ interpolate their answers ...
On Tue, 2 Apr 2002, Richard.Hall wrote:
> Recent discussion here has convinced me that we should never have set up
> NBU s/w compression in the first place. ("Told you so"!!)
>
> Before we turn it off ...
>
> 1) will this affect recovery from existing images?
[JK] No, at least it's not supposed to.
[DH] No
> 2) or mess anything else up?
[JK] Nope
[DH] No
> 3) (For academic interest only, and to make sure I understand what is
> going on)
> Since our DLT7000s are currently managing ~5Mb/sec, I assume that the
> data is currently compressed on the client side, not decompressed again
> on the server side, and the drives are (roughly) achieving no further
> compression. And that, other things being equal, I can now expect to
> see them managing 10 Mb/sec, but with no reduction in backup time.
> Except perhaps in the tail of the backups, where the number of jobs and
> the total data rate is falling.
[JK]
> Maybe not double, but definitely more. I don't run compression and my
> DLT7k's generally run at 8-10MB/sec, but with hw compression that put's
> me at approx. 4-5MB/sec compressed, which is what they should be running
> at. Occasionally I see my filers pushing them to 14MB/sec but those are
> burst speeds. And in fact, backup jobs may run noticeably faster if the
> clients were cpu constrained to begin with. Not having to do
> compression will lighten cpu load tremendously.
[DH]
> What you should see is a bit more compression due to hardware compression
> being more efficient than software compression and you *should* see the
> backups speed up a bit all things being equal. Software compression
> compresses on the Client (like you said) and then sends the compressed
> packets to the server. Sending a stream is more efficient. Speed could be
> 20% or so better but that depends on your LAN.
[LK]
> I wouldn't expect 10MB/s. You might get it, but there's no reason to
> expect it. 2:1 has nothing to do with the real world. You'll also
> need more than 100Mb/s.
OK, my message was over-simplistic. I understand why 2:1 is only
'illustrative'.
And my media server has Gigabit Ethernet (though the clients don't). That
plus a sufficient level of multiplexing ought to give me the bandwidth I
need, I reckon.
Thanks again.
Richard Hall
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