Re: zpool import skips wedges due to a race condition

[mlelstv%serpens.de@localhost (Michael van Elst)]

alnsn%yandex.ru@localhost (Alexander Nasonov) writes:

>When I run zfs import, it launches 32 threads and opens 32 disks in
>parallel, including cgd1 and dk24. But it can't open dk24 while
>cgd1 is still open (it fails with EBUSY).

>I fixed it in the attatched patch by running only one thread. It's
>not the best approach but I'm not sure how to fix it properly.


There are other issues with scanning devices in an arbitrary order,
a parallel scan just makes it worse by adding randomness.

LVM tries to solve this with an optional filter for device names
when scanning for physical volumes.

The root detection code tries to solve this by scanning twice, once
for wedges, once for everything else, and by identifying wedges
that alias a partition.

For a complete solution you would need to know all the device relationships
(dkX on wdY, cgdN on dmN, etc, but also e.g. dkX on cgdN). That still leaves
out hot-plug devices where "upper" devices appear late.