Available space on zfs only half of pool

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Available space on zfs only half of pool

Post by TheRoundOne » Sun Jun 16, 2013 7:05 pm

Hi,

I created a raidz2 pool with 4 4TB disks on Thunderbolt.

The pool is shown as having 14Ti available.

Code: Select all
NAME    SIZE   ALLOC    FREE     CAP  HEALTH  ALTROOT
Data  14.6Ti   236Mi  14.6Ti      0%  ONLINE  -


The filesystem, however, has only 6.94Ti available.

Code: Select all
NAME    USED   AVAIL   REFER  MOUNTPOINT
Data   114Mi  6.94Ti   976Ki  none


Here's the pool info:

Code: Select all
sh-3.2# zpool status Data
  pool: Data
 state: ONLINE
 scan: none requested
config:

   NAME                                           STATE     READ WRITE CKSUM
   Data                                           ONLINE       0     0     0
     raidz2-0                                     ONLINE       0     0     0
       GPTE_FB4FA54C-381F-4602-A349-0F92E7C44CBD  ONLINE       0     0     0  at disk3s2
       GPTE_EE691689-961A-4DF0-8DFB-17033BE83BCA  ONLINE       0     0     0  at disk4s2
       GPTE_2A777653-0FBF-4441-BCA9-8D6D71E1A082  ONLINE       0     0     0  at disk2s2
       GPTE_6CDD5862-12A5-4BDF-964A-E4AEDAE53DC0  ONLINE       0     0     0  at disk5s2


I had created multiple zfs datasets, each showed the same space available.

This is a bit confusing. Did I miss something?

Thanks,
Michael
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Re: Available space on zfs only half of pool

Post by ilovezfs » Sun Jun 16, 2013 9:36 pm

TheRoundOne wrote:I created a raidz2 pool with 4 4TB disks on Thunderbolt.

raidz2 means 2 disks will be devoted to parity data. So you only have 4 - 2 = 2 disks for actual user data.

Assuming each disk has exactly 4TB = 4,000,000,000,000 bytes,
your total size is 16,000,000,000,000 bytes.

To convert to Ti divide by 1024^4
(4 disks * 4000000000000 bytes)/(1024^4) = 14.551915228 which is approximately 14.6Ti

However two disks go to parity data, so you only have
( (4 disks - 2 parity disks) * 4000000000000 bytes ) / 1024^4
= ( 2 disks * 4000000000000 bytes ) = 7.2759576142 which is approximately 7.3Ti

Each data set will show the 7.3Ti available because you could use the space from the common pool of usable data space in whichever one of the data sets you want, unless you set quotas.
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