Performance Problem Postmortem

[Brad Dameron]

> > Things you can do :
> > Make syslog asynchronous - that removes one synchronous write to
> > disk. By default it's sync and that means another hardware write
> > before the call returns.
> 
> As an aside, this problem is Linux-specific, as far as I know. It's a
> pretty bad default. BSD-based systems do not have synchronous syslog
> writes by default, nor does Solaris as far as I can remember (been too
> long since I worked with Solaris on a regular basis).
> 
> > If you are brave, or have suitable battery backed hardware, put the
> > leases file on a ram disk. It must not be on a 'normal' ram disk
that
> > would be lost in a system crash or power failure as that would leave
> > you without a lease file. Generally look at the performance of your
> > disk system as that will be a limiting factor on response rates.
> 
> Leases file on some sort of battery backed RAM disk or RAID is a key
> feature, definitely.
> 

You can get the Gigabyte GC-RAMDISK i-RAM card for around $120. You use
regular DDR400 RAM. Supports up to 4GB. Try to get the 1.3 version.

http://www.gigabyte.com.tw/Products/Storage/Products_Overview.aspx?Produ
ctID=2180&ProductName=GC-RAMDISK

I tested these in our lab and they perform very well. They have SATA-I
connections so it looks just like a drive to the OS. I only tested it
under Linux and Windows. I however could not use them in production due
to going with blades for our infrastructure. They also have a battery
backup on them so you are good for 24 hours without power. 
I then setup a cronjob to sync my leases and logs off the drive every 5
minutes. It did improve performance by about double.

Brad