Where did the space go?

[cybercon_inc]

I have two shelves of 1TB SATA attached to a FAS3020. To get the maximum aggr, I used 19 data disks and 4 parity disks in two RAID-DP groups. The result, a 13.1TB aggr.

I get it that a 1TB HDD becomes 828GB, but how did 19 of 828GB become 13.1TB?

[aborzenkov]

a) Aggregate size is shown base 1024, disk size shown is mixed based 1024/1000 (it is 1024 * 1000 * 1000). The usable size of 1TB disk is 807GiB.

b) 10% of aggregate space is reserved for internal use

c) By default 5% of remaining space is reserved by snapshots (can be set to 0%)

If you compute the result, you get exactly 13109GiB.

[cybercon_inc]

OK. Thanks.

But WRT c), I thought snapshot reserve happens when you create a flexvol, if there is no volumes exists yet, where is this 5% setting coming from? Or, how do I set it to 0 in order to see bigger number of Total Capacity?

[aborzenkov]

There are also aggregate level snapshots.

[cybercon_inc]

After some more googling, I decided to leave this 5% alone. So much for max vol size of 16TB.

[cybercon_inc]

Found this, http://netapp-blog.blogspot.com/2009/06/how-usable-space-in-netapp-array-lun-is.html

[aborzenkov]

This applies to V-Series LUN, not to native disks. You could also look at NetApp kb34044 (although I am afraid they changed document numbers recently).