zfs/raidz and creation pause/blocking

[Eugene M. Zheganin]

Hi.

Recently I spent a lot of time setting up various zfs installations, and
I got a question.
Often when creating a raidz on disks considerably big (>~ 1T) I'm seeing
a weird stuff: "zpool create" blocks, and waits for several minutes. In
the same time system is fully responsive and I can see in gstat that the
kernel starts to tamper all the pool candidates sequentially at 100%
busy with iops around zero (in the example below, taken from a live
system, it's doing something with da11):

(zpool create gamestop raidz da5 da7 da8 da9 da10 da11)

dT: 1.064s  w: 1.000s
 L(q)  ops/s    r/s   kBps   ms/r    w/s   kBps   ms/w   %busy Name
    0      0      0      0    0.0      0      0    0.0    0.0| da0
    0      0      0      0    0.0      0      0    0.0    0.0| da1
    0      0      0      0    0.0      0      0    0.0    0.0| da2
    0      0      0      0    0.0      0      0    0.0    0.0| da3
    0      0      0      0    0.0      0      0    0.0    0.0| da4
    0      0      0      0    0.0      0      0    0.0    0.0| da5
    0      0      0      0    0.0      0      0    0.0    0.0| da6
    0      0      0      0    0.0      0      0    0.0    0.0| da7
    0      0      0      0    0.0      0      0    0.0    0.0| da8
    0      0      0      0    0.0      0      0    0.0    0.0| da9
    0      0      0      0    0.0      0      0    0.0    0.0| da10
  150      3      0      0    0.0      0      0    0.0  112.6| da11
    0      0      0      0    0.0      0      0    0.0    0.0| da0p1
    0      0      0      0    0.0      0      0    0.0    0.0| da0p2
    0      0      0      0    0.0      0      0    0.0    0.0| da0p3
    0      0      0      0    0.0      0      0    0.0    0.0| da1p1
    0      0      0      0    0.0      0      0    0.0    0.0| da1p2
    0      0      0      0    0.0      0      0    0.0    0.0| da1p3
    0      0      0      0    0.0      0      0    0.0    0.0| da0p4
    0      0      0      0    0.0      0      0    0.0    0.0| gpt/boot0
    0      0      0      0    0.0      0      0    0.0    0.0|
gptid/22659641-7ee6-11e6-9b56-0cc47aa41194
    0      0      0      0    0.0      0      0    0.0    0.0| gpt/zroot0
    0      0      0      0    0.0      0      0    0.0    0.0| gpt/esx0
    0      0      0      0    0.0      0      0    0.0    0.0| gpt/boot1
    0      0      0      0    0.0      0      0    0.0    0.0|
gptid/23c1fbec-7ee6-11e6-9b56-0cc47aa41194
    0      0      0      0    0.0      0      0    0.0    0.0| gpt/zroot1
    0      0      0      0    0.0      0      0    0.0    0.0| mirror/mirror
    0      0      0      0    0.0      0      0    0.0    0.0| da1p4
    0      0      0      0    0.0      0      0    0.0    0.0| gpt/esx1

The most funny thing is that da5,7-11 are SSD, with a capability of like
30K iops at their least.
So I wonder what is happening during this and why does it take that
long. Because usually pools are creating very fast.

Thanks.