----- Original Message -----
From: "Terry Carmen" <te...@cnysupport.com>
To: "Brandon Hilkert" <bhilk...@vt.edu>
Cc: "Postfix users" <postfix-users@postfix.org>
Sent: Friday, March 20, 2009 4:40 PM
Subject: Re: Move queue to RAMFS
Brandon Hilkert wrote:
I'm trying to get my queue to ramfs. I mounted a volume. When I send mail
to it, it tells me there's insufficient storage.
Not sure about the error, but in general RAMFS sounds like a bad idea for
a number of reasons including the ability to crash your machine if it
fills up, and the loss of messages if you lose power or have a hardware
failure. The server should use free RAM for cache anyway, so I'm not sure
how much of a performance improvement you'll see.
OTOH, the benchmark data would be interesting.
This is entirely for disk checking. It will be in a data center where power
isn't an issue anyway, so loss of queue isn't a problem.
Also, you might want to check and see where the problem actually is, since
I'd be amazed if postfix is actually disk-bound. It's more likely to be
another process or something with log-level set too high. If it turns out
to be logging and you can't reduce the log data, you could try moving
syslog to a difference machine.
Syslog is waiting to write to the file. I disabled logging entirely which
showed no significant change in performance.
Re: disk relevance - Dave had a different view about that (see response
below)
Postfix performance is primarily limited by how fast the disk can sync data.
For standard rotational disks, this is going to be primarily limited
by how fast the disk rotates. Since your standard SATA disk reotates
at 7200 rpm, replacing it with a disk that spins faster (10k or even
15k RPM) will help immensely. There are 10k SATA disks available,
otherwise you have to go SCSI. Expect up to a 30% improvement with a
10k rpm disk and nearly double with a 15k rpm disk.
If you want to go significantly faster than that, you have 3 options:
1. More spindles and the appropriate RAID setup. A RAID10 array with
4 disks should double your random IO performance.
2. IO controller with battery-backed memory cache in write-back mode.
The battery backed cache will basically allow syncs to happen nearly
instantly (as long as your cache isn't full). This can improve
performance by an order of magnitude.
3. SSD (Solid state disk). Intel makes some great SATA SSDs that will
absolutely fly under this kind of workload. But before you buy any
old SSD, I highly recommend you read this article at Anandtech:
http://www.anandtech.com/storage/showdoc.aspx?i=3531
4. A combination of 1 & 2 or 2 & 3.
Hope this helps.
-Dave
Terry
