Hardware

Hello Experts,

I have few doubts on RAID 5 with LUNs carved as STRIPE and CONCAT

RAID 5 = STRIPE + Parity mirroring

I would like to know if the LUNs carved are CONCATE from RAID 5 disk array. Are the I/Os are spread accross the disks within the RAID 5 Array? And if I do carve STRIPED LUNs on RAID 5 array will it be double striping and will result in serial I/O over the Array?

Thanks,
Syb

I assume by striped LUN's you mean software RAID.
Software RAID is "poor man's RAID".

I assume that you have a hardware RAID5 controller.

There is little point in using both at the same time. Software RAID uses CPU cycles which can be bad on a system loaded with apps.

Originally there was RAID3. This striped the data over a number of drives and also had a dedicated parity drive. This meant that every file write involved a write to the parity drive hence creating a bottleneck. So RAID5 was created.

RAID5 is striped data with rotating parity. The parity function is rotated between all the drives eliminating the bottleneck. I/O is spread across a number of actuators (drives) so the more drives in the RAID5 the greater the I/O bandwidth available. Compounding this functionality with software RAID is pointless. The hardware RAID5 controller will offload all I/O processing (parity calculation) from the main CPU of the box.

Dunno whether that answers you question(s) or not? Post back any further questions if not.

So RAID5 if good for general random I/O (mixed and unpredictable read/write)
In a situation where I/O's are predominantly read-only (eg, large Oracle database with mainly read enquiries) then RAID3 will be a bit faster because there's no need to read the parity if drives are healthy.