I think this might interest you. The magic figure is about 30.
36 -> 30 GB 72 -> 60 GB 144 -> 120 GB 250 -> 180 GB
Although not exactly accurate, for my purposes this has worked out quite well.
The other magic factor is about 0.8
Take a filer with 5 x DS14 shelfs giving 70 drives. Assume that one shelf will be assigned to "overhead", create volumes on the remaining 4 shelf with two parity drives, giving a total of 8 drives overhead. Assume that the system drive takes two drives and 4 drives are reserved as spares (8 + 2 + 4 = 14 drives), leaving 56 drives ( or 80% ) for data.
If you now apply 0.8 again to the remainder it will give you the approximate size of the space available for the file system. (this is a crude approximation of the magic 30 factor). (0.8 x 0.8 = 0.64)
If you now apply 0.8 again to the remainder it will give you the approximate space availabe to the users with a snapshot reserve of 20%. (0.8 x 0.8 x 0.8 = 0.5)
This crude methode has work well for me until now
Bye Ernie
-----Original Message----- From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com] On Behalf Of James Brigman Sent: Thursday, August 19, 2004 2:38 PM To: 'toasters' Subject: RE: usable size of a 146-GB drive
Geoff;
You've done some good research: I'm seeing similar numbers you're finding on 36 and 72GB disks. However, notice that the space efficiency is going to vary dramatically with the size of the RAID group. That should not be surprising: a two-spindle volume's real availability drops to 33%. (48GB / 144GB ... everyone sees that with vol0...)
I believe it's possible, if you make the raid group very large and use RAID-DP, you could increase space efficiency and performance too.
I don't have 144GB numbers for you, but the "250GB" drives in an R200 work out to less than 200GB usable. I'll try to post some numbers to the list later this week...
JKB
-----Original Message----- From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com] On Behalf Of Geoff Hardin Sent: Wednesday, August 18, 2004 8:20 PM To: toasters Subject: usable size of a 146-GB drive
I was just wondering if anyone had any info on the usable size of the 146-GB drives from NetApp. I am trying to figure out how many drives I'll need, but I can't really tell without knowing what my usable space will be.
If it helps, here's some data I have collected from other drives.
18 GB disk - becomes 17.0 GB because of disk overhead (right size) - becomes 14.923389 because of OS overhead - becomes 13.431053 with a 10% snap reserve - becomes 11.938713 with a 20% snap reserve
36 GB disk - becomes 33.917 GB because of disk overhead - becomes 31.776308 because of OS overhead - becomes 27.273826 with a 10% snap reserve - becomes 25.421048 with a 20% snap reserve
72 GB disk - becomes 67.906 GB because of disk overhead - becomes 59.747608 because of OS overhead - becomes 53.772850 with a 10% snap reserve - becomes 47.798088 with a 20% snap reserve
Thanks,
Geoff Hardin UNIX System Administrator Dallas Semiconductor / Maxim Integrated Products geoff.hardin@dalsemi.com It's illegal to walk your elephant without a leash in Wisconsin.