Dell and SSD drives

[John LLOYD]

> >
> >> I am looking at our mail servers and trying to get some disk IO
> >> contentions down. I would like to know if people have used 
> SSD's in a
> >> Linux environment. I am looking at an SSD over a ramdisk for
> >> persistence of storage in case of reboots. What I would 
> like to do is
> >> put in 2 SSD's into a 2950 and have them deal with the malware and
> >> spam scanning directories as that seems to be the 
> contention points.
> >
> > First you should maximize your RAM and try tmpfs.
> > That would be faster.
> >
> 
> It would be, but I have been asked to guarantee persistence 
> over reboots.
> 

Be sure you have optimized your filesystem and mounts too.  You have
options on filesystem type (ext3, XFS, etc), synchronous updates to
files or just to metadata (directories).  And updating, or not, file
access times.  Each of these has an effect on IO rate.  The quick answer
is "-o noatime,nodiratime,async" but your tolerance for noatime depends
on your application.

If your current disks are not full, you can maximize seek performance by
using a minimal partition size in the fast (low sector number) portion
of the disk.  Seeks are shorter and the IO transfer rate is faster.
Leave the rest of the disk unused, or at least very rare usage like /usr
for a dedicated server.

If you have the room or money, put several disks together working in
parallel in a raid-10 stripe set, using either a hardware raid
controller or a Linux software mechanism like MD or LVM.   15k SAS disks
are a lot faster than 7200 RPM SATA disks; your 2950 should support
them. 

(Of course this advice applies to spinning magnetic disks, not SSD of
either variety.)

--John