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Operating System - Tru64 Unix
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Max group size remains 32 Gb in raid5

Jayesh Thakar
Occasional Contributor

Max group size remains 32 Gb in raid5

I am configuring to install 6 drives having 9.1 GB capacity in AS1200 server with RAID5.
I am forced to create only 32 GB sized group inspite of 43 GB(n-1).

How can I create full disk capacity(n-1) group ?
Victor Semaska_3
Esteemed Contributor

Re: Max group size remains 32 Gb in raid5


If I remember correctly, the size restriction you're experiencing is because the RAID controller is a 16-bit controller.

Your only option is to create two RAID-5 sets on the 6 drives. I no longer have a AS1200 so I can't tell you how to do this. I can tell you to do one RAID-5 at a time. If you try to initialize both RAID-5 sets at the same time, you'll probably experience a time-out. The RAID controller does time out if the RAID sets aren't initialized within a certain amount of time. 6 disks will take hours.

From the OS you'll see 2 disks which you put together with the addvol command.

There are 10 kinds of people, one that understands binary and one that doesn't.
Michael Schulte zur Sur
Honored Contributor

Re: Max group size remains 32 Gb in raid5


what kind of controller are you using?
Are you using hardware or software raid?
Is that a mylex controller?


Hein van den Heuvel
Honored Contributor

Re: Max group size remains 32 Gb in raid5

What is important to know is not the server, but rather the controller used in the servers. Sounds like it a 'mylex' SWXCR adapters (KZESC, KZPSC or KZPAC)

The limitation however is on the logical drive set. So you could create a 45 GB group (5*9+9), and divide it up in two logical units each 22 GB. Next you can combine those volumes with either LSM, or AdvFS (voladd).

I would discourage to stripe those units together as that would potentially generate excessive head movements (first blocks in first unit is on outer edge of disks, first blcks of second volume will be close to the middle of the disks.).

Ideally (performance wise) you would keep the usage separate. You'd put high access data in the first set (maybe maxed out at 32Gb) and stick different data (historical, kits, backups, other application, month close data, development copy of db,..) on the second unit (maybe only 10+ GB).