Wait, how much space do I actually have?

All your general support questions for OpenZFS on OS X.

Wait, how much space do I actually have?

Postby Tsur » Tue Jan 19, 2016 10:51 pm

So I built one pool using raidz2 with seven, 4 TB drives. I'm expecting roughly 20 TB.

In 10.9.5, the finder lists 17.91 TB available. Were it reporting TiB, that almost seems correct. But AFAIK, the finder reports terabytes.
zpool list reports FREE 25.2T. That can't be right.
zfs list shows AVAIL 16.3T. That can't be right either.
df -h reports Size 16Ti. Again, not right.

How big is the pool?
Tsur
 
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Re: Wait, how much space do I actually have?

Postby Tsur » Wed Jan 20, 2016 12:25 pm

So I've tried rebuilding the zpool a few time and have gotten the same results.

I also built a raidz2 with only 6 of the 7 drives, expecting right around 16TB.

The finder reports 15.43 TB – this seems very reasonable.
zpool list reports FREE 21.7T – not right, but consistent with removing one 4TB drive.
zfs list shows AVAIL 14T - not right, and not consistent with removing one 4TB drive.
df -h reports Size 14Ti - not right, but kinda consistent with what zfs list reports.

With all of these different results, I feel like I must have some fundamental misunderstanding of space calculation. The only one that makes "sense" is the 15.43 TB reported by the finder. But I don't understand why 6, 4TB drives yields 15.43 TB while 7, 4TB drives yields 17.91. Doing the math, adding one more drive should have yielded something closer to 19.29TB.

Anyone know what I'm doing wrong or what I'm not understanding?
Tsur
 
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Joined: Thu Jan 07, 2016 2:11 pm

Re: Wait, how much space do I actually have?

Postby fissionfan » Sat Jan 30, 2016 8:15 pm

Just a bump because I don't know, but would be interested in the answer.
fissionfan
 
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Re: Wait, how much space do I actually have?

Postby Tsur » Sun Jan 31, 2016 3:54 pm

Thanks for that link. That actually furthered my understanding and clarified some of the inconsistencies I was receiving.

I've actually decided to trust what the finder is reporting. I ended up using ashift=9 when creating the pool and now, supposedly have 19.12 TB of storage.

I stressed about the reduced performance of an ashift value of 9, instead of 12. But some quick testing showed a pretty minimal performance hit: 109 MB/s writes vs 112 MB/s writes. If anything, I think my bottleneck is likely gigabit Ethernet.
Tsur
 
Posts: 10
Joined: Thu Jan 07, 2016 2:11 pm


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