Raid 1+0 is faster than raid 5 if your have a lot of writes to the database. I would guess IBM probably has a Redbook on some of this somewhere for DB2.
> -----Original Message----- > From: McKown, John [SMTP:[EMAIL PROTECTED]] > Sent: Monday, February 10, 2003 2:08 PM > To: [EMAIL PROTECTED] > Subject: Re: raid question > > David et al., > I don't know if it applies to Linux, but I vaguely remember a RAID 1+0 > where > the data is both striped and mirrored. Is this superior to RAID 5? Also, > for > the very paranoid, I would guess that one could use a RAID 5+0 where the > data is striped w/parity like RAID 5, then each RAID 5 volume is mirrored. > This would seem very excessive, but very safe. > > -----Original Message----- > From: David Boyes [mailto:[EMAIL PROTECTED]] > Sent: Monday, February 10, 2003 1:47 PM > To: [EMAIL PROTECTED] > Subject: Re: raid question > > > > I was told that if you lose one volume of a raid set you can replace > > and the data will get rebuilt, but if you lose a second volume before > > you get the first one rebuilt you will lose all the data -- > > irretrievably! Is this true? > > Yes, for RAID 5. While the parity information *is* distributed, it's a > one-dimensional distribution. When that second drive goes and the rebuild > isn't yet complete, you're SOL. In RAID 0 (striping only), lose one and > you're screwed. For RAID 1 (mirroring), they're mirrored pairs, so if you > lose one and then another one, the data is gone and there's nothing to > recover from. > > > Is there any reasonable way to get around it? > > Y-cabled parallel drive arrays like they use in telcom switches and > nuclear > explosion instrumentation, but the price tag is astronomical, so probably > not in the "reasonable" class. 160G of that equipment is well over $750K. > > > Is there > > a reasonable alternative to raid? > > AFAIK, no, not unless you happen to be the Sultan of Brunei and have a > immense quantity of unused cash available with nothing better to do with > it > (and if you do, I'll be happy to give some of it a warm home...). > > - db
