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(this is going to be a bit longer, but since it is a reappearing topic
I'd like to provide some background information on what happens
behind the scene)
Am 26.10.14 um 12:09 schrieb 'Busty' via zfs-macos:
> This generated a follow up question:
> I did the zpool replace with an unformatted disk as described in
> the oracle documentation. After that, zpool status showed the disk
> as part of the pool, but as "disk2", not as "disk2s2". Accordingly,
> OSX wanted to initialize the disk every time upon booting.
> So I formatted the disk as described in the getting started guide
> on MacZFS, which resolves the problem of OSX wanting to initialize
> the disk, but still it shows as "disk2" (without the s2) with zpool
> status. I was prepared to resilver the disk again after that, but
> it was still part of the pool.
> I started a scrub, had 6 checksum errors on that disk right at the
> beginning, but otherwise the scrub seems to consider the data as
> good. It is at 7 percent right now.
> Should I be worried that the data is not integer?
Yes, you should.
You basically did the following:
Gave a whole disk to ZFS, telling it, it is OK to use the whole space
from first to last block of the disk.
ZFS did so and started writing data:
a) it's vdev label 0,1 from block 0 to 1023 (assuming 512 byte blocks)
b) it's vdev label 2,3 from block N-1024 to N-1 (assuming N block on
c) your pool data in between, following it's somewhat complex
Told OS X to write a disk label (aka GPT) on the disk.
OS X did so and started writing data:
a) A protective MBR in block 0 -> no damage, ZFS anticipates
that, leaving block 0 to 32 (16k) of its label alone.
b) The primary GPT structures, starting from block 1 (byte position
512) to end of block 33 (byte position 17408).
This trashed part of the configuration dictionary in vdev label 0
c) The secondary GPT structures, in the last 17408 bytes of the disk,
overwriting part of the uberblock array in vdev label 3.
d) The Mac OS X EFI area, usually around block 40 to 409600 (byte
positions up to 200 MB). This is "/dev/diskXs1".
e) The man partition "/dev/diskXs2", roughly starting at block 409640
and extending until some blocks before the secondary GPT structures.
This is just created but nor written in "noformat" has been used.
What does this mean?
It depends on how ZFS sees the disk. Most likely it will continue to
use "diskX" (no slice). In that case:
The pool keeps functioning, since vdev labels 1 and 2 are undamaged (0
and 3 are overwritten, see above)
ZFS will almost instantly fix it's labels, completely overwriting the
secondary GPT. Mac OS X doesn't care, it writes the secondary GPT and
never looks there again.
The situation on the is start is more complex.
ZFS will also almost instantly fix its label 0. However, this writes
only from block 32 on (byte position 16384 onwards), since it
completely ignores the first 16 blocks (supposed to hold disk
identifier) and doesn't touch the next 16 in normal operation, since
they are supposed to hold ZFS boot code and are unused in current
So the rewritten vdev label 0 trashes the last 512 bytes of the primary
GPT. This does concern Mac OS X and you should see a waring about an
invalid GPT CRC in the system log after boot.
So much for the administrative data structures. What about your data?
ZFS' data area starts after the vdev label 1, i.e. at block 1024
(byte position 512 kB). This is somewhere inside the EFI area,
overwriting whatever Mac OS X placed there (depends on version, older
Mac OS X version didn't placed anything there, don't know for newer
versions). In any case, Mac OS X does not access the EFI area in
normal operation, and so won't note the damage.
On the other hand, Mac OS X is initializing the EFI area when
initializing a disk, placing an empty FAT file system there.
This FAT overwrites part of the ZFS pool data and caused the checksum
What to do now?
I would detach the disk in question, zap the first and last several MB
of disk space (i.e. of diskX itself, not of the diskX2s slice) by
writing zero bytes to disk, for example using "dd", reformat with
diskutil and reattach as /dev/diskX2s.
Another approach for zapping the disk content is, to format as HFS+
with diskutil and then select "clear/erase free disk space" (or
whatever the English button label says).
> On 23.10.14 14:01, 'Busty' via zfs-macos wrote:
>> This was in fact easier than I thought. What did the trick was
>> to physically swap the faulty disk with a new one and then "zpool
>> detach (faulty disk)"
>> After that a "zpool replace" went like a charm.
>> Problem solved.
>> On 15.10.14 20:32, 'Busty' via zfs-macos wrote:
>>> In my pool, I had a disk that got a smart error (bad block), so
>>> I pulled it out, installed a new one and made a "zpool replace
>>> disk5s2 806745480046791602". (That number was shown when typing
>>> "zpool status" as the missing device.)
>>> The resilver process started, but it seems that the new disk is
>>> faulty, because it disappears from the device list
>>> infrequently, but still at least every 6 hours (I have
>>> Temperature Monitor running which shows me all disks by serial
>>> So I want to change it. But zpool detach <poolname> dev/disk5s2
>>> gives the error "no such device in pool".
>>> How can I abort the resilvering process? Or is there another
>>> way to restart the resilvering with a new disk?
>>> The original disk with the bad block is already on its way to
>>> Western Digital (it was still in warranty).
| Bjoern Kahl +++ Siegburg +++ Germany |
| "googlelogin@-my-domain-" +++ www.bjoern-kahl.de |
| Languages: German, English, Ancient Latin (a bit :-)) |
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