Date: Fri, 13 Nov 1998 15:27:47 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: dag-erli@ifi.uio.no (Dag-Erling C. =?iso-8859-1?Q?Sm=F8rgrav?= ) Cc: Marc Slemko <marcs@znep.com>, David Wolfskill <dhw@whistle.com>, hackers@FreeBSD.ORG Subject: Re: dump(8) very slow Message-ID: <199811132327.PAA06232@apollo.backplane.com> References: <Pine.BSF.4.05.9811130909500.12077-100000@alive.znep.com> <199811131747.JAA05198@apollo.backplane.com> <xzp4ss3cptx.fsf@hrotti.ifi.uio.no>
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:Matthew Dillon <dillon@apollo.backplane.com> writes:
:> I gzip -2 the dump output on
:> the remote machine before it comes back through the ssh pipe.
:
:Why not turn on compression in ssh (-C) rather than add an extra stage
:to the pipeline?
I am saving gzip'd dumps to tape directly. I know, I know, it means you'd
better not have a tape error in a dump. Too bad. Exabytes do duel-head
verification anyway, though you definitely have to clean the drives twice
a week (at the volume levels we push through the drives) to maintain
optimal performance (which is 3 MBytes/sec for an exabyte Mammoth).
The backup machine is already cpu-limited doing the encryption (even though
the network is switched and secured, we don't trust it). If I had the
backup machine do compression (ssh -C) as well, or if I had it gunzip
the remotely-gzip'd dump, the 2.5 MBytes/sec would because 1.5 MBytes/sec.
If I have the tape drive do the compression, I get sub-optimal capacity
verses pushing gzip'd dumps to a tape drive in uncompressed mode.
Sometimes I think about turning off ssh's link encryption, but then I think
a little more and say 'nahh, better to leave it on'. Once we upgrade the
machine we'll be able to dump 6 MBytes/sec over the network, which matches
two 3 MByte/sec tape drives very well.
-Matt
:DES
:--
:Dag-Erling Smørgrav - dag-erli@ifi.uio.no
:
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Matthew Dillon Engineering, HiWay Technologies, Inc. & BEST Internet
Communications & God knows what else.
<dillon@backplane.com> (Please include original email in any response)
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