7.3 Disk layout

Disk IO is one of the big performance killers.

Tables and indexes on separate physical disks

Do not use software RAID, remapping, or NFS. One of the worst things you can do for performance is to make the CPU do extra work with each IO or otherwise slow them down. For that reason you should never use software RAID. If you decide that you want to use RAID make sure you use hardware raid. If you do go with raid we would suggest either RAID 1 or RAID 10 for update intensive situations, and RAID 5 for read only, where you want to reduce the cost of disks.

Raid	Description	Results	Recommendation
0	Disk Striping	Very fast read and write	No (reliability)
1	Mirroring	Faster read, normal write	Acceptable
1/0	Striped mirrors	Faster read, normal write	Best Raid to use.
3	Separate Parity disk	Redundancy with high transfer/low transaction rate	No
5	Distributed Parity	High read rate (without failure), slow write rate	For read only tables, maybe. Generally No.

 

You should not use Texis to access a network-mounted database. There are two main reasons. First, the performance of network file systems tends to be poor, as Texis will typically do random seeks and small reads, which does not mix well with NFS. Secondly if you access the database from two distinct machines there will be no concurrency control between the machines, and you will run out of semaphores on both machines very quickly.

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