RE: To RAID or not to RAID? -that is the question...
RAID 5 is not mirrored, it is striped with parity. You do not lose 1/2 the disk space, you lose 1/n of the disk space to parity, with n being at least 3 disks. RAID 5 can give you good performance with reads, but it will probably be slower when you have lots of writes because it takes time to calculate and write the parity. With RAID 5 you can only lose 1 drive per failure. With RAID 1 you could lose more than one as long as it's not a drive in the same mirrored pair. Your best bet is to do your own testing. Your environment plays a big part in the performance. I had a drive array with controllers that would not balance the reads across RAID 1 pairs resulting in terrible performance. In this case I had better performance with from a RAID 5 strip set. Informix has a 1995 white paper called RAID and Informix Databases. It's old but it's a start. Jamie Kohm -----Original Message----- From: Salem Lee Ganzhorn [SMTP:slganzho@unity.ncsu.edu] Sent: Tuesday, July 06, 1999 8:44 PM To: informix-list@iiug.org Subject: Re: To RAID or not to RAID? -that is the question... sandeep.singh@usa.net wrote: : Thanks y'all for your comments/suggestions. I guess : I must be missing something cause I did not get what : a lot of people talked about using RAID5. RAID5 will : no doubt be faster but then there is no redundancy. : Maybe two RAID5 channels and then database mirroring : across the two controllers? : : Will someone please comment on this: Suppose I have : a choice of having one single RAID1/0 (or even just : RAID1) controller OR having two Ultra2 SCSI channels : and then use Informix mirroring across the two cont- : rollers. Which one makes more sense? Raid 5 is mirrored. There is enough data mirrored on the disks so if any one drive goes down you can rebuild the drive completely from the remaining drives. You get the speed of striping plus the fault tolerance of mirroring. Of course you only get 1/2 of the space the drives have to offer. The only downside is you have to have at least 3 drives. Regards, Salem