SUMMARY - Sparc Storage Array Question

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Original question:

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:
Bill Townsley
Cynthia Shang
Vasantha Narayanan
Roger B.A. Klorese
Raju Krishnamurthy
Vinh Tu
Tom Quirt
Ron Loftin
Law Hon Man
David Steen
Rudy Yu

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
----
Jason

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