From: Jaegeuk Kim <[email protected]>
Sent: Tuesday, April 14, 2020 8:09 AM
To: Tim Walker <[email protected]>
Cc: [email protected]
<[email protected]>
Subject: Re: [f2fs-dev] [question] ZBC/ZAC Offline/read-only zone support
On 04/14, Tim Walker wrote:
> Hello-
>
> I am trying to determine how f2fs handles an offline (or read-only) zone when
> it is backed by a host-managed SMR HDD. I haven't been able to find any
> specific code path that places an offline zone into a separate list, or a
> path that checks the zone condition.
Do we support a zone going read-only or offline? Thanks for the info.
Which scenario do we need to see ro or offline zones? Can we expect some
when mounting the filesystem? Or, does setting a zone to readonly happen
in runtime? If we detect them at mount time like former one, we need to
treat the discarded blocks in the zone with unusable space, and set
allocation bits to avoid GC.
>
> Best regards,
> Tim Walker
>
> _______________________________________________
> Linux-f2fs-devel mailing list
> [email protected]
Hello-
A zoned block device HDD zone can transition to Offline or Read_Only at any
time, according to the spec. I don't know if any drive manufacturer transitions
zones to Offline or Read_Only today. I was trying to see what support f2fs has
for zones that end up in that state, since these zone states have been in the
spec from the beginning.
In my mind f2fs would discover that a zone was Offline or Read_Only when f2fs
reads the zone status (write pointers) at mount time, any time f2fs resets a
write pointer during GC, and any other sequence of events that causes a report
zones call. In addition, if a zone were to asynchronously go Read_Only or
Offline f2fs would presumably discover it when it tried to write a Read_Only
zone or any access to an Offline zone. The error codes are descriptive.
If f2fs were to discover a Read_Only zone it could just mark it to never get
GC, since it can't be reclaimed. Thanks.
Best regards,
-Tim Walker
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