Re: Physical disks vs Logical drives for RAID on OracleNT

The redo logs write sequentially to the disk tracks. If you share that read/write head (i.e. physical drive) with any other function, then you will have to seek back to the redo log to continue writing the log.

Since you only have 5 disks, you don't have enough distinct drives to both stripe and mirror the redo logs, and still dedicate the physical volume to the redo logs.

Do you have a write back cache on your RAID controller? If so, I think this helps compensate for a lot of the problems with competing access to disks, assuming that your disk arrangement can keep up with your overall write throughput. I have yet to read any conclusive studies on this though.

I assume you realize that by going with RAID O (no mirroring) for the data files, you will have to recover the database from the backup and archived redo logs if a disk fails, so availability cannot be a high priority.

Given that, if transaction performance is the highest priority, I would use two physical drives in a RAID 1 mirror, with redo, archived redo, OS, oracle software, and whatever else fits. I would then use the remaining three drives as a single RAID 0 volume with the system, temp, data, and rollback tablespaces, and also the primary NT swapfile (put a small one one the RAID 1 mirror for recovery). You might also want to reserve a small part of each disk in the RAID 1 array to be configured as a regular volume for storing redundant copies of control files, etc.

On the other hand, if you can sacrifice the storage space and performance isn't a problem (i.e. you don't have a high transaction load), I'd go with RAID 5 for the three disk array, so that you have some fault tolerance.

John

shan168 wrote in message <7e0kq3$pee$1_at_nnrp1.dejanews.com>...
>Hi,
>
>I have a Compaq Proliant server with 5x4.3gb RAID disks. I have decided to
>configure them to Raid-1 (mirrored set) for redo logs, control files, NT
OS,
>and oracle software, and Raid-0 for data files (RBS, data, temp, ...).
>
>Now my question is: how many PHYSICAL disks should I create? I know Oracle
>recommends as many physical disks as possible. However, according to my
>research, some people say since RAID-0 stripes data accross several disks,
>there is no need to create independent disks, i.e. one large disks with
>several logical drives will be good enough. Which one is correct?
>
>Any suggestions will be appreciated.
>
>S.H.
>
>-----------== Posted via Deja News, The Discussion Network ==----------
>http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
Received on Thu Apr 01 1999 - 16:24:33 CST