> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:owner-u2- > [EMAIL PROTECTED] On Behalf Of Adrian Merrall > Sent: Wednesday, March 05, 2008 4:51 AM > To: [email protected] > Subject: Re: [U2] Hardware upgrade > > Bill said... > > > > Glenn is right. I like disk mirroring. I have seen big problems with > > raid-5. When one of the Raid-5 disks dies, the whole RAID set is > > worthless > > as all of the data on the disks becomes invisible. > > > > Hmmmm - the whole RAID 5 set is worthless when one disk dies? Isn't the > whole point of a raid 5 stripe that one disk can die and the set will > continue just fine albeit with zero redundancy? >
Not worthless, just really slow due to increased reads to obtain data from a single partial parity set. > >From the wikipedia page on RAID (hopefully more accurate than the page on > Jimmy Wales' girlfriend). > > Distributed parity requires all but one drive to be present to operate; > drive failure requires replacement, but the array is not destroyed by a > single drive failure. > > 'nuff said. > > Glen said... > > > > > Why did you choose RAID5? RAID10 offers the redundancy you want from > > RAID5, > > but it won't grind to a snails pace when one of the drives fail. It > > requires > > more drives, but it gives more performance and reliability over RAID5. > > > > > YMMV on this one. I agree RAID 1+0 is better but the last couple of drive > failures I have experienced in a RAID 5 set have not had any noticeable > impact. In fact the raid 5 set has held good performance while providing > disk I/O and allowing the hot spare to bind into the set. Possibly a > slight > drop-off but definitely not snail's pace. > The few RAID5 arrays I've run have been on 3Ware write caching controllers and the only performance degradation from a dead drive wasn't extremely noticeable. But, then again it happened on a randomly used backup file server. A background rebuild didn't make that much of a difference, but then again it wasn't a live database server either. When in doubt, and 24/7 performance is critical, I always use RAID10. I'm not saying RAID5 is a horrid and worthless RAID level. It's just my opinion that RAID10 is better in every aspect, even though an extra spindle or two is needed. > However this is on an EMC San providing storage to RHEL servers so there > is > some serious caching going on there, although, IIRC the SAN will > automatically disable write caching for an array with a failed disk. No > idea what would happen with a raid-5 stripe in the built in scsi > controllers > in an HP DL though. > > Regards, > > Adrian > Auckland, NZ Glen B ------- u2-users mailing list [email protected] To unsubscribe please visit http://listserver.u2ug.org/
