zfs/raidz: seems like I'm failing with math

[Alan Somers]

On Sun, Oct 16, 2016 at 10:56 AM, Eugene M. Zheganin <emz at norma.perm.ru> wrote:
> Hi.
>
> FreeBSD 11.0-RC1 r303979, zfs raidz1:
>
> ===Cut===
>
> # zpool status gamestop
>   pool: gamestop
>  state: ONLINE
>   scan: none requested
> config:
>
>         NAME        STATE     READ WRITE CKSUM
>         gamestop    ONLINE       0     0     0
>           raidz1-0  ONLINE       0     0     0
>             da0     ONLINE       0     0     0
>             da1     ONLINE       0     0     0
>             da2     ONLINE       0     0     0
>             da3     ONLINE       0     0     0
>             da4     ONLINE       0     0     0
>             da5     ONLINE       0     0     0
>
> ===Cut===
>
> 6 disks 960 Gbs each:
>
> ===Cut===
>
> # smartctl -a /dev/da0
> smartctl 6.5 2016-05-07 r4318 [FreeBSD 11.0-RC1 amd64] (local build)
> Copyright (C) 2002-16, Bruce Allen, Christian Franke, www.smartmontools.org
>
> === START OF INFORMATION SECTION ===
> Model Family:     Samsung based SSDs
> Device Model:     SAMSUNG MZ7KM960HAHP-00005
> Serial Number:    S2HTNX0H507466
> LU WWN Device Id: 5 002538 c402bdac1
> Firmware Version: GXM1003Q
> User Capacity:    960 197 124 096 bytes [960 GB]
> Sector Size:      512 bytes logical/physical
>
> [...]
>
> ===Cut===
>
> But:
>
> ===Cut===
>
> # zpool list gamestop
> NAME       SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP HEALTH  ALTROOT
> gamestop  5,22T  4,38T   861G         -    24%    83%  1.00x ONLINE  -
>
> ===Cut===
>
> Why 5.22T ? If zpool is displaying raw size, it should be 960 x 6 = 5760 Gb
> = 5.65 T. If it's displaying the actual data, then it should be 960 x 5 =
> 4800 Gb = 4.68 T. 5.22 T is neither of these. I'm stuck, please explain. :)
>
>
> Thanks.
>
> Eugene.

It's raw size, but the discrepancy is between 1000 and 1024.  Smartctl
is reporting base 10 size, but zpool is reporting base 1024..
960197124096.0*6/1024**4 = 5.24 TB, which is pretty close to what
zpool says.

-Alan