[cvsnt] performence problem

[Peter Crowther]

> From: Stéphane Nicoll [mailto:Stephane.Nicoll at bsb.com] 
> 2) What kind of disks (ATA, SATA, SCSI) and disks speed?
> 
> SCSI 15k rpm (3x36 Gb RAID5) 

Presumably configured as a single array?  There aren't enough drives to make multiple RAID5 arrays...

> 5) Are CVS repository and temp directories set on the same 
> disks? Moving 
> the temp folder to another disk may help to reduce head "trashing".
> 
> Not on the same logical drive (temp is on c:, repository on d:)

This will make the situation worse, not better, if the drives are configured as a single array.  Now the disk heads must move between space on two partitions, which is almost guaranteed to be further away than if the files were on the same partition.  Separating files onto different partitions to reduce head contention only works if the partitions are on different sets of physical disks*.

However, it does give us an opportunity for a little more monitoring - Stéphane, if you monitor logical disk activity rather than physical disk activity, which partition is getting most of the traffic?  This may help us to determine whether it's the repository or the temp space that's the bottleneck.

I suspect we're optimising the wrong thing here, however.  *Something* is causing all this traffic to the disks; we should go back to the application and try to find out what.  Stéphane, what's the pattern of CVS use at your organisation?  In particular, do you have automated systems that update or commit regularly, or do you have paranoid developers who update several times an hour?  Basically, it seems odd that there's this much server traffic.

		- Peter

* My gold-plated (and very expensive!) drive configuration for this kind of heavily loaded system would be:
- Mirrored pair of drives for boot and system partitions
- Mirrored pair of drives for swap
- Mirrored pair of drives for CVS temp
- RAID '10' (duplexed RAID 5) for repository - or, if performance is your *absolute* requirement, duplexed RAID 0 and watch like a hawk for disk failures!
For extra points, make the mirrors duplexed, i.e. on different controllers.