On 2015-01-05 12:31, Lennart Poettering wrote: > On Mon, 05.01.15 10:46, Harald Hoyer (har...@redhat.com) wrote: > >> We have BTRFS_IOC_DEVICES_READY to report, if all devices are present, so >> that >> a udev rule can report ID_BTRFS_READY and SYSTEMD_READY. >> >> I think we need a third state here for a degraded RAID, which can be mounted, >> but should only after a certain timeout/kernel command line params. >> >> We also have to rethink how to handle the udev DB update for the change of >> the >> state. incomplete -> degraded -> complete > > I am not convinced that automatically booting degraded arrays would be > a good idea. Instead, requiring one manual step before booting a > degraded array sounds OK to me.
I think that a good use case is when the root filesystem is a raid one. However I don't think that the current architecture is enough flexible to perform this job: - mounting a raid filesystem in degraded mode is good for some setup but it is not the right solution for all: a configure parameter to allow one behavior or the other is needed: - the degraded mode should be allowed only if not all the devices are discovered AND a timeout is expired. This timeout is another variable which (IMHO) should be configurable; - there are different degrees of degraded mode: if the raid is a RAID6, losing a device would be acceptable; loosing two devices may be unacceptable. Again there is no a simple answer; it is needed a configurable policy; - pay attention that the current architecture has some flaws: if a device disappear during the device discovery, ID_BTRFS_READY returns OK even if a device is missing. I proposed a mount.btrfs helper[1], which (IMHO) is a good place for this kind of job. However I have to point out that both Chris, and David aren't fully convinced of this solution. I hope that they could change opinion. In conclusion, I see some use case to allow to mount a degraded btrfs filesystem; however I don't see as viable the idea to enhance the BTRFS_IOC_DEVICES_READY ioctl. More logic is required. > > Lennart > BR G.Baroncelli [1] http://www.spinics.net/lists/linux-btrfs/msg39706.html -- gpg @keyserver.linux.it: Goffredo Baroncelli <kreijackATinwind.it> Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
