Hi there. I've got a Sparc Storage Array, full of 2 gig disks, and I
had a question about RAIDing it. After going through all of the
documentation, I couldn't find a formula which would tell me how much
disk I should expect to get out of a RAID 5 filesystem. How can I
find out how large I can make the filesystem?
Thanks go to:
Roger B.A. Klorese
Law Hon Man
Here are a couple of the answers I got back:
---- There is a command that's part of the Veritas Volume Manager package. If you have that package running, you can do this for any disk group you have configured... vxassist -g group_name maxsize layout=RAID-5 This will tell you the maximum size that disk group has to offer in a RAID-5 configuration.
- Bill Townsley
---- (RAID5 with logging) # vxassist maxsize layout=raid5 disk88 disk89 disk90 disk91 Maximum volume size: 8304640 (4055Mb) (RAID5 without logging) #vxassist maxsize layout=raid5,nolog disk76 disk77 disk78 disk79 Maximum volume size: 12455936 (6082Mb) (Striping) # vxassist maxsize layout=stripe disk01 disk02 disk03 disk04 disk05 Maximum volume size: 20762624 (10138Mb)
- Cynthia Shang
---- If the log is put on one disk, that leaves 5. You use 1/nth of the disks for parity... in this case, 1/5th, so you get 8GB worth of data. (2GB drives hold more than 2GB, actually.) When Sun ships Volume Manager 2.3, you'll be able to select the disks and hit the "maxsize" button and let the software fill un the size.
- Roger B.A. Klorese ---- Most of the RAID Level 5 system will take about 20% of total "RAW Capacity" to be the overhead. This will leave about 80% of your "Raw Capacity" be the RAID Capacity. (Raw Capacity = # of Drive * hard drive capacity of each drive). In your case, your "Raw Capacity" is 12 GB (6 * 2GB), so your RAID Capacity is about 9.6GB (12GB * 80%). Most of the RAID system allow you to create multiple LUs (Logical Unit) and the OS will "see" these LUs as logical drives. Solaris can handle 1TB (1024GB) of file system, so you will be fine with this 9.6GB RAID. - Rudy Yu
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