SAN disk performance verses Internal Disk

[Shivkumar]

Hello,

Are SAN storage disk more faster than internal attached disk ?
I believe all SAN are connected through Fiber Channel and internal disks are never connected through Fibre Channel and hence maybe much slower than SAN.

Thanks,
Shiv

[Uwe Zessin]

What do you define as 'faster'? MegaBytes per second?

There is no general rule. Performance depends on a number of factors.

I've seen reports here on ITRC that a local disk or RAID array in a specific situation was faster than an expensive external Fibre Channel array. Now, those arrays are usually designed for many small concurrent I/Os while some people like to test for single-stream MegaBytes/second.

There are also some situations where a 'cheap' SATA disk drives can offer more MegaBytes/second than a 'high-performance' Fibre Channel disk - the secret in that case was different disk geometries and densities.

[Víctor Cespón]

You have 2 limits here:

1) Number of disks. Each disk can handle a certain amount of MB/s and I/Os per second. It does not matter if it's IDE, SATA, SAS, FC, Firewire... An array of 50 disks beats an array of 5 disks anytime.

2) Connection. The data from/to the array has to go though a controller and a link. It can be:

- Parallel SCSI: 320 MB/s per channel
- SATA: 150/300 MB/S to each drive
- SAS: 300 MB/s to each drive
- FC: 100 - 800 MB/s per link
- iSCSI: 10 - 100 MB/s per link

So an array of SAS disks attached locally can be faster than the same number of disks on a SAN storage device, yes. SAN is nor for speed, is for sharing storage and provision it on demand.