topic Disk Array FC60 in Disk Enclosures

Disk Array FC60

Kathy McGohan_1 — Wed, 10 Jan 2001 20:10:41 GMT

We have a N-Class system in which the customer wants it configured, striped 4, Raid 3. We usually use Raid 5.
I'm not sure why they want Raid 3. I know they have a lot of data to load.
I believe the FC60 supports a Raid Level 1+0. Can anyone tell me for sure and how is a Raid Level 1+0 configured. I heard it is better than Raid 5. Is this true? Does a 1+0 use mirroring?
Thanks in advance.

Re: Disk Array FC60

Insu Kim — Thu, 11 Jan 2001 01:12:25 GMT

Hello
Raid 1/0 is a combination of Raid 0 and Raid 1.
Remember that Raid 0 uses striping to achieve igh performance and Raid 1 uses hardware mirroring to obtain data redundancy.
Speed advantage of striping plus redundancy advantage of mirroring are combined together.
A Raid 1/0 LUN caontains an even number of disk drives from 4 to 30 disks.
One half of the disks are primarys and the other half are mirrors.
For High availability, each disk in the pair must be in a different enclosure.

There're three ways of configuring the array as Raid 1/0 on FC60.
One is manually, another is to use sam and the third is through STM.
A simple example of manually configured Raid 1/0 is as follows.

Syntax:
#amcfg -L : -d,....... -r
#amcfg -L B:1 1:3,1:4,2:3,2:4 -r 1 -s 4 arrayID
If you select RAID 1 with more that 2 disks, then Raid 1/0 is created.
This example shows that the LUN is owned by controller B, is assigned LUN number 4 and stripe segment size is 4 Kbytes.
Please note that example selects disks in seperate enclosures to create mirrored pairs.

You can do this throughout both sam and STM.

Regards,

Re: Disk Array FC60

Kathy McGohan_1 — Thu, 11 Jan 2001 13:14:48 GMT

Thanks In-Su Kim.

I just received an email from the customer stating that Oracle responds better under RAID 3 than RAID 5.
Is this true? Because I thought RAID 5 was better than RAID 3.

Re: Disk Array FC60

Tim Medford — Thu, 11 Jan 2001 16:14:13 GMT

Kathy - When it comes to "reading" data, RAID5 is the same speed as other RAID levels, but when it comes to writing data, it is the slowest of all the RAID configurations.

I would never put an Oracle database in RAID5 (especially the redos and archives), unless it was a read-only DSS type database that gets loaded periodically.

I'm not sure what they are trying to acheive with the RAID3, I would stick with the RAID 1/0 if you have the space for it, it's the fastest.

Tim

Re: Disk Array FC60

Kathy McGohan_1 — Thu, 11 Jan 2001 18:03:32 GMT

Tim, thanks. If we cannot go with RAID 1/0, what would be the next solution, RAID 3 or RAID 5? We will be installing Oracle 8.1.6.

Re: Disk Array FC60

Tim Medford — Thu, 11 Jan 2001 20:49:02 GMT

Honestly I haven't used RAID3 before so I would just be guessing rather than basing my answer on experience.

Here's a link do a document which describes RAID in detail. Maybe it can help answer your question:

http://www.uni-mainz.de/~neuffer/scsi/what_is_raid.html