Load spikes when new email arrives

[Blake Hudson]

francis picabia wrote the following on 1/25/2013 7:55 AM:
>
> On Thu, Jan 24, 2013 at 12:22 PM, Blake Hudson <blake at ispn.net 
> <mailto:blake at ispn.net>> wrote:
>
>
>
>     There are a couple suggestions I'd like to put forth. First, improper
>     partition alignment is generally masked by the controller cache. I
>     strongly encourage you to check that your RAID array is making use of
>     this cache by enabling the WriteBack caching option on this array,
>     especially if your PERC card has a BBU (I think this was optional on
>     perc 5). You can install the MegaCLI tool from LSI to verify this (can
>     also be checked from OpenManage or reboot into the controller BIOS).
>
>
> Thanks for this tip.  It put me on to what is wrong.
>
> Jan 18 07:25:39 myserv Server Administrator: Storage Service EventID: 
> 2335  Controller event log: BBU disabled; changing WB virtual disks to 
> WT:  Controller 0 (PERC 5/i Integrated)
>
> Bingo!  We had write back all along, and the performance tanked when it
> fell back to write through.  I was wondering why my policy change attempts
> were flipping back when I tried testing WB this morning!
>
> This explains everything we've been seeing.  Wow.  Gotta call Dell.
>
> Thanks everyone for the assistance.  I didn't think a battery which 
> shows OK
> status in omreport could wound us!
>
>
The PERC cards will disable write-back caching while the BBU is 
charging/exercising. However, within a few hours the BBU should return 
to normal status. In rare instances, people on the Dell mailing list 
have reported that their caching status never returns to write-back - 
even after attempting to force write-back caching on the array. Attempts 
and power cycling or firmware flashing are tried, but seem to be futile 
in most cases. Often, replacement of the card is necessary. I'm unsure 
if it's the battery, the card, or some software setting, but I would 
definitely follow up with Dell.

On the next server (or array) you configure, I would attempt to align 
your partitions as you've investigated. Sector 2048 seems to be a good 
starting position for most RAID levels. I have no conclusive evidence 
that a different file system or alignment improves my performance, 
because I've never done a fair side by side test with controlled inputs. 
However, we use ext4 and do align our partitions using RAID10 on 15k SAS 
drives for all our Cyrus installs. I have found some issues with the 
newer systems that I attribute to the move from ext3 to ext4 which can 
result in MySQL replication problems on power loss/freeze, but these 
issues are vary rare and usually easy to recover from in our 
environment. I also notice that new systems always perform better than 
the old systems, even with identical hardware - I've often attributed 
this to fragmentation.

--Blake
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.andrew.cmu.edu/pipermail/info-cyrus/attachments/20130125/ae67af35/attachment.html