RE: Fwd: RE: RAID or NOT to RAID?

Now that's a post :)

"Do not criticize someone until you walked a mile in their shoes, that way when you criticize them, you are a mile a way and have their shoes."

Christopher R. Spence OCP MCSE MCP A+ RAPTOR CNA Oracle DBA
Phone: (978) 322-5744
Fax: (707) 885-2275

Fuelspot
73 Princeton Street
North, Chelmsford 01863  

-----Original Message-----
Sent: Thursday, August 09, 2001 3:11 AM
To: Multiple recipients of list ORACLE-L

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. <Ctrl-A> 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_at_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"
> <denmark_weatherburne_at_ho To: Multiple
recipients of list ORACLE-L
> tmail.com> <ORACLE-L_at_fatcity.com>
> Sent by: cc:
> root_at_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_at_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_at_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).
-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: Christopher Spence
  INET: cspence_at_FuelSpot.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_at_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).