-Daedalus Posted January 23, 2021 Share Posted January 23, 2021 (edited) Hi all, Sanity check here. I removed two drives that had been cleared of data (ls -la showed 0 on each drive). I stopped the array, new config, kept parity and cache slots. Assigned everything back, removing drives 6 and 7, moving everything after slot 5 up two slots. Enter encryption passphrase, tick parity is valid, start array. All came back fine, all data is there. Run parity check, and lots of errors, as if it's recomputing everything. My understanding was if there was no data on the drives, parity shouldn't have to be rebuilt. At this point if I have to rebuild parity that's fine - not the end of the world - I just want to make sure I haven't made a massive oopsie. Thanks! server-diagnostics-20210123-1343.zip Edited January 23, 2021 by -Daedalus Quote Link to comment
trurl Posted January 23, 2021 Share Posted January 23, 2021 5 minutes ago, -Daedalus said: My understanding was if there was no data on the drives, parity shouldn't have to be rebuilt. Your understanding is incorrect. An empty disk is not a clear disk. Probably faster to rebuild parity than to correct it now. Quote Link to comment
-Daedalus Posted January 23, 2021 Author Share Posted January 23, 2021 Good to know. I assumed drive with no data = zeroed drive, therefore wouldn't affect parity. The wiki mentions running a clear-me script, but it doesn't mention doing anything special with the drives. I assume it adds a flag in the drive header or something as well? Quote Link to comment
remotevisitor Posted January 23, 2021 Share Posted January 23, 2021 "No data" in this case means every sector on the disk contains zeros (so the the parity calculations remain valid when they are removed) in your case you have a file system on the disks showing no files .... the file system structure are data. Also if you used to have files on the drive then the content of the files are almost certainly still there .... it is just the directory entry describing where the file is the was deleted. so an empty file system is not the same as a disk containing just zeros. Quote Link to comment
trurl Posted January 23, 2021 Share Posted January 23, 2021 Parity doesn't know about files, only about bits. When you delete a file most of the bits related to the file are unchanged. It is basically just marked as reusable space and not connected to the folder structure any longer. Quote Link to comment
-Daedalus Posted January 23, 2021 Author Share Posted January 23, 2021 I wouldn't mind, but I just gave a presentation last week on ZFS. You'd think I've have remembered that file level and block level are different things. I blame the beer. Thanks guys, blonde moment of the day. Hopefully the only one. Quote Link to comment
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