Re: 64-btrfs.rules and degraded boot

[Goffredo Baroncelli <kreijack@inwind.it>]

On 2016-07-06 20:57, Chris Murphy wrote:
[...]
> 
> Seems like we need more granularity by btrfs ioctl for device ready,
> e.g. some way to indicate:
> 
> 0 all devices ready
> 1 devices not ready (don't even try to mount)
> 2 minimum devices ready (degraded mount possible)
> 
> 
> Btrfs multiple device single and raid0 only return code 0 or 1. Where
> raid 1, 5, 6 could return code 2. The systemd default policy for code
> 2 could be to wait some amount of time to see if state goes to 0. At
> the timeout, try to mount anyway. If rootflags=degraded, it mounts. If
> not, mount fails, and we get a dracut prompt.
> 

Pay attention that to return 2, you have to scan all the VGs to check if all the involved devices are available: i.e. a filesystem composed by 5 disks, may have a VG RAID5 with only 3 disks used for data, and a VG RAID1 for metadata for the other two disks....

Think to try to perform this for each disk appearing.... I fear that it is too expensive


> That's better behavior than now.
> 
>> Equivalent of this rule is required under systemd and desired in
>> general to avoid polling. On systemd list I outlined possible
>> alternative implementation as systemd service instead of really
>> hackish udev rule.
> 
> I'll go read it there. Thanks.
> 
> 


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