On Tue, Sep 18, 2012 at 9:53 AM, Timothy J Massey <tmas...@obscorp.com> wrote:
>
>
> All of that was clearly outlined at the top of the e-mail: 4 x 2TB
> Seagate SATA drives in RAID-5 (using md, which I''m not sure I stated
> originally).
Raid5 has its own reasons for bad write performance. You sort-of make
up for it with 8+ drives in an array, but with 4 you've basically made
all the heads wait for the slowest and forced a read-update-write
cycle on everything less than a raid block in size. And with md, the
parity update is probably going to be clocked as CPU, not device i/o
time. Keep this in mind when comparing backuppc vs. native rsync -
backuppc is storing metatdata in different places, updating multiple
directory entries, etc. That translates to more small writes. For
the extreme case, consider a native rsync of an unchanged tree - no
writes at all, where backuppc will build a new directory tree and
touch the link count in every inode.
>
> That's fairly bad news for me, then. These are embedded-style
> motherboards, and upgrading to a >3GHz Xeon processor is not an option...
> :(
There is not just a little bit of difference between a dual-core box
and the new xeons. I don't have benchmarks, but they are insanely
faster. Throwing some more RAM at it might help a little by
permitting more read-ahead and write buffering but probably just a
little if you aren't seeing much wait time now.
> That's my next step. When I upgraded from my old VIA-based servers, I
> (accidentally) left compression on, and thought the new, dual-core, faster
> and more efficient processor would be OK with this. That may have been my
> biggest mistake. (Honestly, I've already found other areas that make me
> think that my original distain for compression might have been
> well-justified! :) )
I don't think it will matter that much once you have passed the 2
fulls to get cached checksums. After that you'll only be
compressing/uncompressing content with changes.
--
Les Mikesell
lesmikes...@gmail.com
------------------------------------------------------------------------------
Live Security Virtual Conference
Exclusive live event will cover all the ways today's security and
threat landscape has changed and how IT managers can respond. Discussions
will include endpoint security, mobile security and the latest in malware
threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/
_______________________________________________
BackupPC-users mailing list
BackupPC-users@lists.sourceforge.net
List: https://lists.sourceforge.net/lists/listinfo/backuppc-users
Wiki: http://backuppc.wiki.sourceforge.net
Project: http://backuppc.sourceforge.net/
