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Re: [BackupPC-users] BackupPC speed and some basic questions
2009-03-06 22:45:58
The CPU is hit most by the comrpession scheme when using cpool, then by the rsync checksums and then by the ssh session. If you use an IDE interface or a SATA in IDE mode then you will be using more CPU. If you are not using DMA and your disks are stuck in PIO (do hdparm /dev/disk0 to see) then you are really going to eat up CPU cycles.
You might also have a slow drive controller.
The bump in CPU and RAM was obviously a good thing. More ram allows linux to be more swappy and frees up more ram for the system to use in disk caching.
I did something to my machine recently that did wonders for my backup performance. I baught an Adaptec PCIe Raid card (31205) with 256MB of cache. The 8x PCIe interface completely removes a bottleneck there, the cache is awesome for I/O as it buffers I/O latency which backuppc is very vulnerable too. I migrated my old 4 disk raid5 into a 5 disk raid5ee which is a fancy way adaptec uses a hot spare to improve performance.
My backup times dropped from about 3 hours to well under 2. something like a 40% improvement. Considering it is still a 4 disk raid5 + hot spare and the drives are comparable this is a rather huge gain.
On Fri, Mar 6, 2009 at 6:56 PM, Adam Goryachev <mailinglists AT websitemanagers.com DOT au> wrote:
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Reinhold Schoeb wrote:
> you were right. I added 2 Gigs of RAM and a new CPU (Athlon 5050e, dual core,
> 2.6 GHz). Now I get about 23 MB/sec transfer speed, which results in 16 hours
> for a full backup.
>
> So finally I have to say that BackupPC is very dependent on CPU power.
Don't forget that some HDD interfaces are very CPU intensive, so you may
use 40% CPU just to deal with the IO, plus you need CPU to handle your
network interface, plus you also need CPU to do the compression of file,
SSH encryption, etc....
Also, you might like to check your memory usage during a backup, mainly
to ensure that you are not using any swap space (anything more than a
couple of megs swap space will mean you need more RAM)...
Regards,
Adam
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