[SAC] New Vms w/ Debian 7

[Martin Spott]

On Fri, May 09, 2014 at 04:12:52PM -0700, Alex Mandel wrote:

> Aside from switching from Raid 6 to Raid 5 what else would improve this?

Foremost I'd like to make clear that at least my *primary* concern is
*not* to talk about technologies but instead it is to make a clear
distinction beween cause and effect.  Thousands or maybe millions of
servers are being backed up while in service without getting the users
into trouble, but our VM's do get into trouble.
I'd like to avoid creating the impression that the backup is the
culprit.  No, it's not, instead the disk system is, because ....  and
then we can start talking about the details.  If we confuse cause and
effect, then people are probably going to draw false conclusions over
and over and we hardly can stop it.

> My understanding is that Raid 6 should not be significantly slower for
> read operations than Raid 5 but I have no real world data for that.

I'd say the key to more I/O performance is eliminating the HW RAID
controller and using really fast (15k) drives.  We're having a wild mix
of read and write operations of different sizes and according to my
experience the OS does better optimization these days than a HW
ontroller would do.  Moreover there's fewer latency if we remove the
intermediate step - which the HW controller actually is.
I've done a couple of conversions from HW RAID to direct disk access
(sometimes still using the same host controller but for pass-through
disk access only) and I regret none of them.

> XFS, ZFS or BTFS instead of ext3?

Ah, yes, please let's eliminate Ext3  :-)

Cheers,
	Martin.
-- 
 Unix _IS_ user friendly - it's just selective about who its friends are !
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