Yechial, > You have 12 disks. In raid 0+1 you use striping across 6 volumes. > In raid 5 you strip across 11 disks, so you get almost double the work
They didn't tell you everything they know about RAID 0+1. The disks may be striped into 6 logical disks, and they are written to as 6 logical disks, but when reading, all 12 disks are read from independentantly. So a RAID 5 is not actually doing more work a READ. But during a write, it's doing quite a bit more than RAID 0+1. > without returning and moving the r/w head on the same disk. Maybe if there is one user on the system, doing 1 read. Multiuser IO systems don't serialize the IO, at least not to the extent that the single user scenario requires. This is much like reorging a table so that all data is in a 'contiguous' space. It's an illusion, it doesn't really work that way. Jared On Sunday 03 November 2002 08:03, Yechiel Adar wrote: > Hello Ian > > I heard a lecture on raid 5 disks a few weeks ago. > The rational behind read 5 being faster then raid 0+1 is this: > You have 12 disks. In raid 0+1 you use striping across 6 volumes. > In raid 5 you strip across 11 disks, so you get almost double the work > without returning and moving the r/w head on the same disk. > > Yechiel Adar > Mehish > ----- Original Message ----- > From: MacGregor, Ian A. > To: Multiple recipients of list ORACLE-L > Sent: Friday, November 01, 2002 2:48 AM > Subject: RE: Re Raid 5+ > > > I cannot fathom Raid 5 being faster than Raid 1 tor writes. The real > question is, is it fast enough for your users. We happen to have a 650 > terabyte database here. Even using Raid 5 disk storage would be > prohibitedly expensive. So we use a home-built hierarchal storage system > and store much of the data on Redwood tape drives. Users know that > requesting data from the Redwood drives will take some time. But they > were told to expect that. (The database is Objectivity not Oracle, and I > have nothing to do with it). The online data as opposed to the near-line > data is stored in Raid 5 arrays. > > What I don't know is what percentage of Oracle databases can run fine on > Raid 5 vs. Raid 1. It would not surprise me if the answer was well over > 50% > > Ian MacGregor > Stanford Linear Accelerator Center > [EMAIL PROTECTED] > -----Original Message----- > From: John Hallas [mailto:john.hallas@;hcresources.co.uk] > Sent: Thursday, October 31, 2002 12:34 AM > To: Multiple recipients of list ORACLE-L > Subject: Re Raid 5+ > > > Jared, > > > > We are certainly going to be performing extensive testing to ensure > performance of our applications under Raid5+ is acceptable. > > > > That means it is as good if not better than that experienced under > Raid1 > > > > As I see it Oracle gain no benefit for stating that Raid5 should be > used if they did not believe that to be the case. If there was any doubt it > would be easier fro them to leave things as they were > > > > > > John ---------------------------------------- Content-Type: text/html; charset="iso-8859-1"; name="Attachment: 1" Content-Transfer-Encoding: quoted-printable Content-Description: ---------------------------------------- -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Jared Still INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
