Is RAID5 better for performance when SQL Server Clustering and SAN is involved?

One of the recent usergroup meeting brought an interesting question that "what type of hardware I need for a RAID-5 Shared Array for SQL Server Cluster"?

By default RAID5 hardware controller is best to hold as not to go with software RAID5 as it will be single-point-of-failure. When you talk about RAID5 on hardware then by default you'll need an external storage array. As per the configuration it is not possible to use a direct attached RAID on one of the servers, because what if that server goes down? A cluster is not much use if you can't access storage when half the cluster goes down. In this case better to look at the SAN (MSA-1500) as low-cost (comparatively) as one of the option with shared SCSI disks (MSA 500), also make sure you have checked with DELL & IBM sites too. As you may be aware that RAID5 is better option for READ (70) and WRITES (30) when configured. In the recent times hardware vendors such as HP/DELL/IBM are selling pre-configured bundle of DL580 class servers with a connected shared storage array using a SCSI that are classed as Packaged Cluster. ONe of the Vendor expert referred me this link on external SCSI disk shelf that connects to your boxes via SCSI HBAs.

Further SCSI drives are built with far higher standards giving much better reliability and longer MeanTimeBetweenFailures than SATA drives. Also the NAS - Network Attached Storage devices as opposed to direct attached storage. You should consider factors for the solution depending upon the High Availablity options and when using Clustering. It comes down to performance again. Also there is a real-time factors in differentiating SCSI to beat SATA when it comes to random I/O, for the large projects within SAN.

As usual RAID 5 is good for database storage if your database is like most where it's mostly read from, not written to. RAID 5 is a bit slower for writes but most databases are read from more often than they are written to. Best practice is also to have the database transaction logs should go onto a separate RAID 1 volume because the logs are written to sequentially - therefore RAID 1 would involve less hard drive seeking because it is writing to the next block (one after the other). When you have the Web Application to host approx 50-200 customers where each customer stores their user configuration in a SQL DB then best to go with RAID5.

Further refernece on MSA drives that it can connect with fibre optic cables, as it will have 1 or 2 controllers, which each connect to a fibre switch. Each host also connects to the switch via a cable and Fibre Host Bus adapter which needs to be installed. By default SAN involvement is costly when compared to SCSI when you have a smaller database and recommendation is to go with RAID 10 - as compared to good choice in a large database environment too.