SLUG Mailing List Archives
Re: [SLUG] Performance Tuning
- To: slug@xxxxxxxxxxx
- Subject: Re: [SLUG] Performance Tuning
- From: Daniel Pittman <daniel@xxxxxxxxxxxx>
- Date: Sat, 06 Sep 2008 12:14:34 +1000
- Organization: I know I put it down here, somewhere.
- User-agent: Gnus/5.110006 (No Gnus v0.6) Emacs/23.0.60 (gnu/linux)
"Tony Sceats" <tony@xxxxxxxxxxx> writes:
> Actually I was under the impression that this was a vanilla on-disk
> backup - ie, something akin to dumping tgz's onto a server with
> reliable disks (hence RAID5)..
It could be, but that is a pretty uncommon model in my experience.
> I must say though that I am surprised that a tape feeder is faster
> than disks to the point of having to maintain a large buffer, but then
> the last time I was responsible for any tape system was with a single
> DDS4 tape drive..
You poor thing. ;) Seriously, though, the tape streamers are not faster
than disks in the same class: you can find plenty of enterprise level
U320 / SAS SCSI disk systems that can comfortably supply an LTO4 device.
You start to hit problems when folks want to do this on the cheap, so
back their system with large, slow 7200 or 10K SATA disks on SAS or SATA
controllers; there you really do need to stripe to keep up.
> backup management is the curse of systems admin imho, so I avoid it at
> all costs - it's horribly mundane and prone to break at will (but we
> all thank the great bit keeper when we need them!)
> I was also under the (unreasearched) opinion that incremental change
> analysis was performed on the client side, not the backup server side,
> although I suppose that backing a large number of similar servers would
> result in a lot of the same files being written a lot of times (eg /lib), so
> it would be smart to only have one copy of the file and a reference for each
> backup that includes this file.. this would certaintly be done on the server
This depends enormously on your backup software; BackupPC and the
various rsync-and-hard-links based backup systems tend to put a lot of
load on the server side.
> but really the point of the above is that you're almost certaintly
> right if you're talking about enterprise backup solutions, and that
> more to the point, the precise backup solution/software chosen will
> drastically change how you tune the server, which is actually what we
> were both saying, so it's a case in point
In my experience there isn't /that/ much difference between "enterprise"
and "home" backup strategies, except the order of magnitude: you face
the same sort of performance issues that an LTO4/SAS array user does
with your SATA/DDS.
You just face them slower: your tape device needs less MB/second to keep
it streaming rather than scrubbing, but your disks are also slower and
busier, so you have the same sort of dramas with keeping the device fed.
In my experience, of course, which doesn't mean that /everyone/ is going
to face these same issues.
 Well, maybe not with DDS, but with tape hardware that is reasonably
affordable by home users in this day and age, such as LTO, AIT