From paled@home.com Wed, 08 Aug 2001 23:20:41 -0700 From: Paul Drake Date: Wed, 08 Aug 2001 23:20:41 -0700 Subject: Re: Fwd: RE: RAID or NOT to RAID? Message-ID: MIME-Version: 1.0 Content-Type: text/plain Hi all. I've been disconnected for awhile - found myself out in Nebraska. Installing 81715/Win2000 on a new Dell PowerEdge 2500. Only had 6 drives on 1 IO channel configured as 3 "containers" - RAID 1. The front grille reminds me of an electric shaver. It was the kinda trip that ended with me pulling a hamstring while unplugging a power cord for my notebook. Gotta stay hydrated and get that daily banana for potassium. repeat after me ... RAID 10 != RAID 0+1 RAID 0+1 != RAID 10 Even with only 4 drives, when they might seem the same, RAID 0+1 is stripe first, then mirror. RAID 10 is mirror first, then stripe. As someone once said, the best way to tell how its configured, is to pull a drive out of a hot swap bay, put it back in and see how many drives re-silver. A corollary would be - pull one drive - and then pull another non-adjacent drive (e.g. in the other cage). If its RAID 01 - you're completely hosed. So much for non-destructive testing. :) oh yeah, and "it depends". If you only need 8KB or 64 KB blocks at one time, go for neither, and just separate files onto different RAID 1 volumes of 2 disks each. If you're daring, don't even bother to use hardware RAID for the online redo logs - and just duplex them with multiple log members of a redo log group. After you locate what your point of contention is - either move the hot spots out to dedicated drives, or add more drives to the volume that has the most I/O. If you need massive amounts of data from full table scans - go for deeper stripes. Even numbers of drives in a volume are preferable for RAID 0 stripes, odd for RAID 3,5. This makes it easy to calculate the stripe depths as a multple of the db_block_size and OS io_size in your head. Gaja wrote a great section on this topic in the Performance Tuning 101 Book. And you can "fix" the RAID configuration by simply deleting the existing RAID config - and starting from scratch. I had a site where a Dell Tech took a perfectly good 4 x RAID 1 (8 drives) config and turn it into a single RAID 0+1 config. at boot gets you into where you can wipe it clean and start from scratch - assuming that you can wipe the slate clean. And I'll beat Joe T to the punch - since you're going to have to re-install the OS - Dell boxes run Linux pretty well. Just that Dell still sucks badly for calling RedHat Linux "Linux 7" on their store website. That still pisses me off. Linux != RedHat. Paul tday6@csc.com wrote: > > In a previous job I had to deal with this issue. WinNT 4.0 on a dual > processor Dell box with 24G of RAID. I had specified RAID 0 + 1 but > "someone" knew better and got it with RAID 5 (5 is obviously better than > 0). The SA wouldn't or couldn't reconfigure and the job needed to get > done. > > It was for a decision support system (basically read-only) and it may be > that sort of a system is less impacted. I abandoned any thought of OFA. > Just stick all the datafiles out on one directory branch (makes cold > backups easier) and let the RAID sort out the contention. > > I didn't like it because I was basically trusting to someone else's > decisions but performance was adequate and the task was successful. I'm > not sure that this would be true with an OLTP system. > > I've seen the notation RAID 10 (which is RAID 0 + 1). Perhaps we should > standardize on that. Obviously RAID 10 has to be twice as good as RAID 5. > Right? > > > "Denmark Weatherburne" > list ORACLE-L > tmail.com> > Sent by: cc: > root@fatcity.com Subject: Fwd: RE: RAID or >NOT to RAID? > > > 08/08/2001 02:47 PM > Please respond to > ORACLE-L > > > > Hi DBA's, > > I hope I'm not opening a can of worms, but I'd like your feedback on the > issue of using RAID 5 on NT 4.0 with Oracle 8.0.5. -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Paul Drake INET: paled@home.com Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru@fatcity.com (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).