Brent,
Brent Wagner wrote:
> Can someone point me to a document describing how available space in a
> zfs is calculated or review the data below and tell me what I'm
> missing?
>
> Thanks in advance,
> -Brent
> ===
> I have a home project with 3x250 GB+3x300 GB in raidz, so I expect to
> lose 1x300 GB to parity.
>
> Total size:1650GB
> Total size using 1024 to measure: ~1534 GB
>
> Expected raidz zpool size after losing 300 GB to parity: ~1350 GB
> Expected raidz zpool size using 1024 to measure: ~1255.5 GB
>
> Actual zpool size: 1.36T
>
> Single zfs on the pool - available size: 1.11T
>
> I realize zfs is going to have some overhead but 250 GB seems a little
> excessive...right? I thought maybe the zpool was showing all 6 disks and
> the filesystem reflected the remaining space after discounting the
> parity disk but that doesn't add up in a way that makes sense either
> (see above). Can someone help explain these numbers?
>
> Thanks,
> -Brent
>
When you say "3x250 GB+3x300 GB in raidz" do you mean:
1) # zpool create mypool raidz 250gb-1 250gb-2 250gb-3 300gb-1 \
> 300gb-2 300gb-3
or
2) # zpool create mypool raidz 250gb-1 250gb-2 250gb-3 \
> raidz 300gb-1 300gb-2 300gb-3
As I understand it, #1 would waste the extra 50gb on each 300gb drive and give
you 1500gb usable space. 250gb of that (1/6th) would be parity, so 1250gb
"data" space.
#2 would make 2 vdevs of 750gb and 900gb totaling 1650gb space. Parity would
use 250gb from the 1st vdev and 300gb from the second; so 1100gb of "data"
space is available.
Either way, when you list raidz* pools with
# zpool list
you see the total physical space. When you list the filesystems with
# zfs list
you get the usable filesystem space, which is where the parity is implemented.
Here's an example with 250MB files and 300MB files:
For #1 scenario:
# zpool create -f mypool1 raidz /250d1 /250d2 /250d3 /300d1 /300d2 /300d3
# zpool list
NAME SIZE USED AVAIL CAP HEALTH ALTROOT
mypool1 1.44G 145K 1.44G 0% ONLINE -
# zfs list
NAME USED AVAIL REFER MOUNTPOINT
mypool1 115K 1.16G 40.7K /mypool1
# zpool status
pool: mypool1
state: ONLINE
scrub: none requested
config:
NAME STATE READ WRITE CKSUM
mypool1 ONLINE 0 0 0
raidz1 ONLINE 0 0 0
/250d1 ONLINE 0 0 0
/250d2 ONLINE 0 0 0
/250d3 ONLINE 0 0 0
/300d1 ONLINE 0 0 0
/300d2 ONLINE 0 0 0
/300d3 ONLINE 0 0 0
------------------------------------------------------------------------------
And for #2:
# zpool create -f mypool2 raidz /250d1 /250d2 /250d3 raidz /300d1 /300d2 /300d3
# zpool list
NAME SIZE USED AVAIL CAP HEALTH ALTROOT
mypool2 1.58G 157K 1.58G 0% ONLINE -
# zfs list
NAME USED AVAIL REFER MOUNTPOINT
mypool2 101K 1.02G 32.6K /mypool2
# zpool status
pool: mypool2
state: ONLINE
scrub: none requested
config:
NAME STATE READ WRITE CKSUM
mypool2 ONLINE 0 0 0
raidz1 ONLINE 0 0 0
/250d1 ONLINE 0 0 0
/250d2 ONLINE 0 0 0
/250d3 ONLINE 0 0 0
raidz1 ONLINE 0 0 0
/300d1 ONLINE 0 0 0
/300d2 ONLINE 0 0 0
/300d3 ONLINE 0 0 0
errors: No known data errors
-------------------------------------------------------------------
Does this describe what you're seeing?
Craig
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