Les Mikesell <lesmikes...@gmail.com> wrote on 11/02/2011 11:25:26 AM:
> > I thought 1 GB would be enough? Or do I just need a larger swap
> file/partition?
>
> I'm sure there are systems running with less, but I like to use 4GB or
> more because the unused portion becomes filesystem cache and greatly
> reduces the disk seeks you need.
Les and I argue frequently about this. I run a dozen backup servers with
512MB RAM, and they do *zero* swapping. So if you're running out of RAM,
it's not BackupPC's fault. And I do not think that more RAM will help
performance with human-sized backup servers. I've even previously posted
to the list the results of going from 512MB of RAM to 2GB of RAM. My
backups still took the exact same amount of time to complete.
Caching the filesystem is *vitally* important for performance. But that
can be done in a very small amount of RAM. Assuming a single file entry
requires 100 bytes (which seems very high to me), 300MB of RAM performing
caching (which is what my backup severs usually average) will hold 3
*MILLION* files.
Now, if you're dealing with a pool in that neighborhood, then *yes*, have
at least 1GB of RAM. But for the rest of us, even 512MB of RAM is plenty.
Having said all of that, my use of 512MB of RAM dates back hardware
limitations of the embedded-style motherboards I use for my backup
servers. If you're using a motherboard that accepts multiple DIMM's of
reasonable density, spend the $50 and get 2 x 2GB DIMM's and eliminate
that as a problem! :)
(And another reason to have more RAM: fsck of a large disk will require
large amounts of RAM. One of my 512MB backup servers with a 1.5TB or so
pool on a 2TB EXT3 partition needed to run fsck. It would crash without
completing it until I upgraded to 2GB of RAM. So don't be stubborn like
me: add more RAM! :) )
> Swap might keep the process from
> failing, but if you use it regularly it will slow the system down
> drastically.
*Drastically*. As in unusuably drastically. Not to start a religious
war, but for the most part the days of swap are over. I don't care how
much RAM you have, if you have a swap file of 1GB residing on a single
SATA spindle and you're actually using all 1GB, your system will be
unusable *anyway*, so who cares if it crashed a little sooner? (The only
exception would be for very long-running processes with a very slow memory
leak: it might keep your system up and running a little longer. But it's
certainly a case of papering over a bug, nothing more.)
> One thing that does consume a lot of memory is using
> rsync backups of targets with a very large number of files, because
> the complete directory listing is sent first and held in memory as the
> files are checked. You might want to set $Conf{MaxBackups} to 1 if
> it isn't already to limit concurrent runs.
While we're on that subject,, how many files are on the system that you're
trying to back up?
Timothy J. Massey
Out of the Box Solutions, Inc.
Creative IT Solutions Made Simple!
http://www.OutOfTheBoxSolutions.com
tmas...@obscorp.com
22108 Harper Ave.
St. Clair Shores, MI 48080
Office: (800)750-4OBS (4627)
Cell: (586)945-8796
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