Networker

Re: [Networker] NetWorker Client Woes

2008-10-01 14:14:39
Subject: Re: [Networker] NetWorker Client Woes
From: Tim Mooney <Tim.Mooney AT NDSU DOT EDU>
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Date: Wed, 1 Oct 2008 13:12:20 -0500
In regard to: [Networker] NetWorker Client Woes, JGillTech said (at 8:11pm...:

[quote="Peter Viertel"]


In theory I suppose if you only allow two ports then it would not be
possible to have more than one backup session at a time (generally
inadvisable anyway) and it may be a problem having a restore and a
backup running at the same time.

Are you saying that backing up multiple save sets simultaneously is not
good form?

I too would be interested to hear Peter's defense of that comment, as I
think it's a generalization that doesn't apply in many situations.

It used to be that you didn't want to have too many savesets all *writing*
to the same tape volume on the server, because that would have a big
impact on doing a restore.  Even in that case, though, it was perfectly
valid to actually have a high device parallelism, as long as you knew the
risks or planned on untangling the savesets later via cloning.  Also, if
you're not using tape for your (initial) backup, then the savesets either
aren't getting interspersed or the fact that they are interspersed doesn't
matter anyway.

Another of the old arguments against a high client parallelism is that
if you have e.g. 4 filesystems on the client but they're all coming off
the same physical disk, then backing them up in parallel would actually
hurt performance (both on the host and of the backup duration), because of
disk head contention.  Maybe that was true for full backups, but for
incrementals or differentials where little has changed, I don't think
there's much evidence to support that.  The disk heads do end up sweeping
back and forth across the platters, but that's not always a performance
killer.

These days, plenty of clients get their storage from multiple sources
(e.g. local disk(s) for the OS, SAN for certain data volumes), so backing
them up in parallel makes plenty of sense.  Now the problem has become
that client A and client B might both get storage from the same set of
physical disks, so backing up one saveset on each of them at the same time
might cause more disk contention than backing up two savesets from one of
them.

Finally, in the days of 10 Mb hubs and half-duplex connections, if one
volume's data could fill your network pipe back to the server, it didn't
make sense to have multiple filesystems competing for the network
resources.  Network bandwidth can still be an issue, but most networks
these days can handle having a client send multiple data streams in
parallel.

Tim
--
Tim Mooney                                             Tim.Mooney AT ndsu DOT 
edu
Enterprise Computing & Infrastructure                  701-231-1076 (Voice)
Room 242-J6, IACC Building                             701-231-8541 (Fax)
North Dakota State University, Fargo, ND 58105-5164

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