RE: General RAID5 question - dangers?

I keep hearing complaints about parity verification. I have a question. From my understanding of mirroring, it does not verify that the data on both disk is the same. Couldnt the same issue occur in a mirrored environment? I thought RAID 3 was the only level that checked parity. Will P.S. I make no claims at being a RAID expert. >===== Original Message From "Obnoxio The Clown" <obnoxio@hotmail.com> ===== >From: douginmaryland@my-deja.com >> >>We are currently working with XP256, HP/UX 10.2, Business Copy, Raid5, >>etc. 3.2 terrabytes raw and have no issue whatsoever with RAID5 in a >>very similar environment. It's a great product, but I'd be curious as >>to what kind of problems you've been having, etc. > >What's a great product? The XP256? How does it perform? How long have you >had it? > >My biggest problem with RAID 5 is that it never verifies the parity it's >written. >________________________________________________________________________ >Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com ------------------------------------------------------------ This e-mail has been sent to you courtesy of OperaMail, as a free service from Opera Software, makers of the award-winning Web Browser, Opera. Visit us at http://www.opera.com/ or our portal at: http://www.myopera.com/ Your free e-mail account is waiting at: http://www.operamail.com/ ------------------------------------------------------------

I've seen RAID 1 implementation which does not compare 2 copies in process of reading data. It simply reads one half from one disk and second half from another, so (in case of partial media failure) situation is very similar to RAID 5. Best regards, Sergey William Rice <ricew@operamail.com> wrote in message news:8hrc8n$9aa$1@news.xmission.com... > > I keep hearing complaints about parity verification. I have a question. > From my understanding of mirroring, it does not verify that the data > on both disk is the same. Couldnt the same issue occur in a mirrored > environment? > > I thought RAID 3 was the only level that checked parity. > > Will > > P.S. I make no claims at being a RAID expert.

Wouldn't parity verification on RAID-5 seem redundant since the "reverse" of the parity should be the actual user data written. If the parity is incorrect, then the data would also be incorrect and if so, would be of greater concern than the parity data itself? RAID-1 whether hardware or software RAID needs to verify that data is identical on both volumes (hence mirrored). If the data is not identical on both volumes and a disk fails, data integrity is compromised and implementing a RAID-1 solution would not be useful. As for the XP256, the array is cache centric. Therefore all reads and writes hit the cache first and then serviced to the host/disk. As RAID- 5 is much slower in writes, it is generally not preferred in database environments where a large number of writes is done. However, the XP256 will read the entire RAID-5 stripe to cache memory regardless of the size of the read/write. All read's and writes are then serviced from cache memory until the array decides to de-stage the stripe to disk. The XP256 can accomodate RAID-1 and RAID-5 within the same array for environments that require it. For maximum tuning, certain heavily hit volumes "hot spots" can be permanently locked in cache using a special software package for the XP256 - all writes/reads to this area (possibly redo logs) can be serviced directly from cache memory... In article <8hrc8n$9aa$1@news.xmission.com>, William Rice <ricew@operamail.com> wrote: > > I keep hearing complaints about parity verification. I have a question. > From my understanding of mirroring, it does not verify that the data > on both disk is the same. Couldnt the same issue occur in a mirrored > environment? > > I thought RAID 3 was the only level that checked parity. > > Will > > P.S. I make no claims at being a RAID expert. > >===== Original Message From "Obnoxio The Clown" <obnoxio@hotmail.com> ===== > >From: douginmaryland@my-deja.com > >> > >>We are currently working with XP256, HP/UX 10.2, Business Copy, Raid5, > >>etc. 3.2 terrabytes raw and have no issue whatsoever with RAID5 in a > >>very similar environment. It's a great product, but I'd be curious as > >>to what kind of problems you've been having, etc. > > > >What's a great product? The XP256? How does it perform? How long have you > >had it? > > > >My biggest problem with RAID 5 is that it never verifies the parity it's > >written. > >_______________________________________________________________________ _ > >Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com > > ------------------------------------------------------------ > This e-mail has been sent to you courtesy of OperaMail, as a free service from > Opera Software, makers of the award-winning Web Browser, Opera. Visit us at > http://www.opera.com/ or our portal at: http://www.myopera.com/ Your free e-mail > account is waiting at: http://www.operamail.com/ > ------------------------------------------------------------ > > Sent via Deja.com http://www.deja.com/ Before you buy.