Free Space Summary

[LeftyAce]

Hi All,

I have a RAID-Z set up with 3 2TB harddrives. This should give me approximately 4TB of usable space (minus the 1000 to 1024 conversion and formatting). I have three datasets defined on one pool, all compressed with LZ compression.

In the daily summary emails that freenas sends out, it says "checking status of zfs pools"
Size: 5.44T, Alloc: 993G, Free: 4.47T.

Where on earth is it getting that 4.47T free number? Is it related to the fact that when I run df it shows each dataset's available space as 2.9T, so it's triple-counting the free space? (Even that doesn't add up). Is there any way to get an overall space summary that's accurate, or do I have to run df and add up the used space manually?

Thanks in advance,

-Lefty

 

[cyberjock]

It sounds like you have a RAID0 zpool. Paste the output of 'zpool status'.

 

[LeftyAce]

[root@freenas ~]# zpool status
pool: myPool
state: ONLINE
scan: scrub repaired 6.56M in 0h57m with 0 errors on Thu Dec 6 17:39:07 2012
config:

NAME STATE READ WRITE CKS
UM
myPool ONLINE 0 0 0
raidz1-0 ONLINE 0 0 0
gptid/b7cd4fb5-3e6f-11e2-b38c-0030487ad448 ONLINE 0 0 0
gptid/b8d66c09-3e6f-11e2-b38c-0030487ad448 ONLINE 0 0 0
gptid/dd3748f8-3fe3-11e2-8275-0030487ad448 ONLINE 0 0 0

errors: No known data errors

 

[jgreco]

The ZFS *pool* has 4.47T free space because the *pool* is 5.44TB (3 2TB drives minus overhead). That only vaguely relates to usable space. If you didn't have compression enabled, you would find that if you write a 1TB file that the free space reported on the pool drops by about 1.5TB. Get it?

 

[LeftyAce]

Aha, thank you! Now that I look at it more closely, I'm noticing that my total used space is about 661GB, but that summary tells me I've allocated 993GB. So the percentage used in that summary is accurate, since it's counting all disks but it's also counting space used for parity information as well as the files themselves. Thanks noobsauce!