Re: Question on changing from ufs to aufs+coss

[Chris Robertson <crobertson@xxxxxxx>]

Pandu E Poluan wrote:
> I see.
>
> About "different disks", must this be different physical disks or 
> different partition is sufficient?
>
> Rgds,
>
> [p]

To give a real world example, I have a server with four cache disks 
(500GB SATA), running Squid2.7STABLE6, with two separate disks (250GB 
SATA) in a RAID1 for the OS and logs.  Load was pretty high with 4 140GB 
aufs cache directories (on ext3 mounted noatime, nodiratime) and 200 
requests per second (peak).   IO wait hovered around 50-60%, with a 5 
minute load average around 5.  I added a 5GB COSS partition to each 
drive*, (so each drive now has a 5GB raw COSS partition, and a 140GB 
aufs partition on ext3, mounted noatime, nodiratime) and saw a dramatic 
reduction in both IO wait and load (IO wait hovers around 5%, and load 
is rarely above .2).  Using a COSS file on the same partition as the 
aufs directory was not beneficial, nor was using a COSS file on a 
separate ext3 partition on the same disk.

For what it's worth, none of this has had much effect on my reported 
median service time.

Chris

*cache_dir coss /dev/sdc1 5120 max-size=51200 max-stripe-waste=32768 
block-size=4096