Re: RAID 1/0 vs. RAID 5

Posted in 1998

Mike South — Tue, 28 Jul 1998 00:22:04 GMT — source: Informix-list mailing list archive (1991-1998)

"Art S. Kagel" <kagel@bloomberg.net> wrote: >Mike South wrote: >> >> I don't know about the Compaq RAID controller so I cannot say for >> sure, however if it is a "smart" controller with read/write caching >> RAID 5 should outperform RAID 1/0, because it automatically does >> parallel reads AND writes are not adversely affected. > >Mike, any RAID 1/0 implementation worth the name also performs parallel >reads and in addition can read from both sides of the mirror of each >pair of drives so that there is MUCH less head movement and drive >contention than in RAID 5. Also RAID 1/0 is almost 2x as fast as RAID >5 for writes and protects your data from bad media which RAID 5 cannot >do. RAID 5 only saves you from catastrophic drive failure of a single >drive. With RAID 1/0, properly set up with each side of the mirrors on >separate controllers and power supplies you can loose a controller or >power supply or up to 1/2 of your drives and still be running with VERY >little degredation. In addition, recovering RAID5 from a single drive >failure reduces performance up to 90% during recovery while a single >drive RAID 1/0 failure will degrade performance during recovery by AT >MOST (100 * 1/N)% where N is the number of mirrored pairs in the stripe >set. While I agree that recovery is slow in a RAID 5 array and that 1/0 offers the level of protection, I would bet that in normal circumstances the performance is a toss up. That, in conjunction with the administrative difficulties of manual fragmentation leads me to lean towards RAID 5 for MOST applications. Truth is this guy's disk layout is pretty irrelevant from a RAID perspective anyway, either will give him very satisfactory performance provided his indexing and database design strategies are properly done. Mike South Producer/Director "Mike South's Peaches & Cream" "Mike South's Georgia Peaches" http://www.mike-south.com Winner 1997 AVN Best Amateur Video Winner 1998 AVN Best Amateur Video Winner 1996 Rocky Mountain Oyster Readers Poll Best Pro-Am Series