Btrfs has been deprecated?

Posted Aug 3, 2017 8:30 UTC (Thu) by Wol (subscriber, #4433)
In reply to: Btrfs has been deprecated? by quotemstr
Parent article: Red Hat Enterprise Linux 7.4 released

Sorry, I don't get it.

md-raid works at the partition level. It knows nothing, cares nothing, about the file system above it so even if you sent a discard to md it wouldn't have a clue what to do with it.

Cheers,
Wol

Btrfs has been deprecated?

Posted Aug 8, 2017 15:39 UTC (Tue) by meuh (guest, #22042) [Link] (2 responses)

FS -> (DM ->) MD -> HDD

If FS initiate TRIM request (discard), beside forwarding the request to HDD, MD can record that one or more stripe are not storing useful information any more (such flag would be invalided by a write on the stripe). Going to the status of each stripes during recover, MD can process only the useful part of the RAID array.

Btrfs has been deprecated?

Posted Aug 9, 2017 7:45 UTC (Wed) by matthias (subscriber, #94967) [Link] (1 responses)

This would work for large TRIM requests. However, TRIM requests are at block granularity. To properly track, which stripes have valid data, MD would need to store for each block whether it has valid data. Otherwise, it cannot tell whether some TRIM request has removed the last used block from a stripe.

Btrfs has been deprecated?

Posted Aug 13, 2017 14:47 UTC (Sun) by Wol (subscriber, #4433) [Link]

And, not being a storage device, MD does not see this as its responsibility.

Yes, it might be a nice addition, but it's added complexity, and it would need somebody to step up to the plate and implement it (plus it would require mucking about with the layout - there may or may not be somewhere to store the fact that stripes are empty or in use).

Cheers,
Wol