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Question and Answer

Tom Kyte

Thanks for the question, Gu.

Asked: January 08, 2002 - 8:56 am UTC

Last updated: April 06, 2005 - 7:00 pm UTC

Version: 8.1.6

Viewed 1000+ times

You Asked

Hi Tom,

We have a new server IBM RS/6000 7025-6F1 with AIX 4.3.3. The disk size is 18GB for all 14 disks. The disk for OS and Oracle software is mirrored and both have seperate Wide/Fast-20 SCSI I/O Controller. FOr the rest 12 disks, we use IBM SSA 160 SerialRAID Adapter(14109100). We will use RAID 0+1. Now the questions are:

1. What is the better way to do RAID 0+1? Strip 5 disks and mirror or strip 2 disks and mirror them? Should we have 2 none RAID disks?

2. Our DB is in no archive mode and exported every week day. How to distribute all datafiles? We will locate password file, parameter file and init.ora file to the disk that ORACLE_HOME reside; put system segment, data segment, index segment, rollback segment to RAID 0+1 disks; put temp segment, redolog file and export dump files to none RAID disks. For rollback segment, I am not sure where is the better place. Could you explain in detail?

Thank you in advance.

Best Regards,
Gu Wang

and Tom said...

1) it depends, go with what you feel comfortable with. The size of the stripe set is up to you (i would actually ask the hardward vendor for their advice on the best performing configuration with their hardware)

see also
</code> <code>

2) why??? do you want to lose a days work? I can assure you that running in this mode is a 100% way to lose data.

Also, export is a very very very poor backup tool. I would STRONGLY encourage you (like REALLY strongly) to rethink your position. Use archive log mode, use hot backups, use export once or twice a week more as a way to test the integrity of your database then as a backup tool. Keep at least 3-5 backups available for recovery purposes.

I really wish you would rethink this, unless you don't care about losing data and can afford to take a very very long time to recover from any errors (if you are able to recover at all).


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Tianhua Wu, January 08, 2002 - 11:59 am UTC

Why not use RAID 1+0 (or RAID 10), it provide much beter protection than raid 0+1.

Tom Kyte
January 08, 2002 - 2:09 pm UTC

excellent explanation from
</code> <code>

The RAID ?hierarchy? begins with RAID 0 (striping) and RAID 1
(mirroring). Combining RAID 0 and RAID 1 is called RAID-0+1 or
RAID-1+0, depending on how you combine them. (RAID 0+1 is also called
RAID-01, and RAID-1+0 is also called RAID-10.) The performance of
RAID-10 and RAID-01 are identical, but they have different levels of
data integrity.

RAID-01 (or RAID 0+1) is a mirrored pair (RAID-1) made from two stripe
sets (RAID-0); hence the name RAID 0+1, because it is created by first
creating two RAID-0 sets and adding RAID-1. If you lose a drive on one
side of a RAID-01 array, then lose another drive on the other side of
that array before the first side is recovered, you will suffer complete
data loss. It is also important to note that all drives in the
surviving mirror are involved in rebuilding the entire damaged stripe
set, even if only a single drive was damaged. Performance during
recovery is severely degraded during recovery unless the RAID subsystem
allows adjusting the priority of recovery. However, shifting the
priority toward production will lengthen recovery time and increase the
risk of the kind of the catastrophic data loss mentioned earlier.

RAID-10 (or RAID 1+0) is a stripe set made up from N mirrored pairs.
Only the loss of both drives in the same mirrored pair can result in any
data loss and the loss of that particular drive is 1/Nth as likely as
the loss of some drive on the opposite mirror in RAID-01. Recovery only
involves the replacement drive and its mirror so the rest of the array
performs at 100% capacity during recovery. Also since only the single
drive needs recovery bandwidth requirements during recovery are lower
and recovery takes far less time reducing the risk of catastrophic data


Bala, April 06, 2005 - 2:41 pm UTC

What are the advantages of RAID 01 over 10? Looks like none to me as RAID 10 provides the same performance of RAID 01 and also high availability. Am I missing missing something Tom?

Tom Kyte
April 06, 2005 - 2:44 pm UTC

nope, not as far as I know (but this is by far not my area of expertise)

A reader, April 06, 2005 - 4:04 pm UTC

Do you have (or know) of a good white paper on preparing a solid backup and recovery plan? I've read the OTN documentation, even taken the Oracle DBA exams, however, in my opinion they don't always prepare you for what you may encounter in the "real world".


Tom Kyte
April 06, 2005 - 7:00 pm UTC

well, the answer is "it depends"

if you are truly into continous operations, it might be:
</code> <code>

or it might just be:
a) hot backup & archives
b) offsite it

or it might be
a) data guard physical standby
b) backups offsite of the standby

or .... depends on your requirements. There are rules of the game like you need to have at LEAST 3 or 4 backups (and all archives), never just backup over the same tape, buy new tapes if you use them -- even if they appear to be working OK, and of course --- do restores on a regular basis, just to make sure you can and know how.