> At what level does OpenAFS implement CoW? Is it implemented at > whole-file-level, i.e. changing a file that is part of a replicated / > backup volume it will copy the entire file, or is it implemented at > some range or smaller granularity level (i.e. it will change only that > range, but share the rest)?
I don't know. I suppose at the file level. > Can one force OpenAFS to do a verification of these checksums and > report back any issues? That is what happens by default. FileLog and SalvageLog should have info on that. In case of failure detection, the volume is taken offline (not taken online again) which manifests in access errors. > What kind of checksums are these? Cryptographic ones like > MD/SHA/newer or CRC-ones? I don't know. I would try investigating in the direction of the fileserver and salvager documentation. > Granted, RAID is not a backup solution, but it should instead protect > one from faulty hardware. Which is exactly what it doesn't do 100%, > because if one of the drive in the array returns corrupted data, the > RAID system can't say which one is it (based purely on the returned > data). Granted, disks don't just return random data without any other > failure or symptom. If you have faulty hw, only a backup and new hardware will save you, but do what you must. > With regard to file-system scrubbing, to my knowledge, only those that > actually have checksumming can do this, which currently is either > BTRFS or ZFS. You only lose data checksumming. Metadata checksumming (and CoW for metadata changes) is still used and gives you most of the relevant properties (because AFS does its own data checksumming). > I think that barriers have other implications especially to journaled > file-systems. They don't. The ones you have in mind relate to local devices. An NAS will simply always report write success as soon as possible (for the sake of covering up the huge network latencies). Your local FS driver will never know the truth... This said, a journaling FS can be less safe over network than a non-journaling FS. > This is true. It is true even of OpenAFS backup volumes. :) That's not true. AFS knows about its backup volumes but not about BTRFS snapshots. At least in principle... Kind regards, –Michael _______________________________________________ OpenAFS-info mailing list OpenAFS-info@openafs.org https://lists.openafs.org/mailman/listinfo/openafs-info
