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  • Re: Converted EXT4 is Slow to Check

    From Borax Man@boraxman@geidiprime.invalid to comp.os.linux.misc on Sun May 10 12:28:31 2026
    From Newsgroup: comp.os.linux.misc

    On 2026-05-09, Rich <rich@example.invalid> wrote:
    Borax Man <boraxman@geidiprime.invalid> wrote:
    On 2026-05-08, Lawrence DrCOOliveiro <ldo@nz.invalid> wrote:
    On Fri, 8 May 2026 12:38:44 -0000 (UTC), Borax Man wrote:

    If you want a robust system which can repair without a backup, you
    can always use parchive, which can store parity data allowing you to
    check AND repair up to a certain amount of damage.

    parchive is the sort of thing IrCOm thinking of. Because it doesnrCOt
    matter how many redundant copies of a file you have, if an error
    happens in the same block on all of them, yourCOre stuffed. Using the
    PAR2 format (erasure code) gets around this.

    However it doesn't work as well for large directory trees, and if
    you do decide to 'parchive' a whole folder, and you need to delete
    or update a file, you have to compute it all again.

    Surely you donrCOt update your backup snapshots in-place, you create new >>> ones. Once a backup snapshot is made, you shouldnrCOt go around fiddling >>> with it. Either keep it or, if itrCOs been obsoleted by a newer one,
    throw it away.

    I use DAR for backups, and it has an option to run parchive over the
    backup file. Backups are incremental.

    I use parchive also for my home photo collection. One I fill a folder,
    I run parchive and make it all read-only.

    Which works very well for "bit rot" situations (the "silent data
    corruption" events).

    But does not help at all if the files that have been parchived and the parchives themselves all reside on one disk, and that disk itself fails
    to the point it is inaccessible. If you can't read the disk you can't
    read the files, even to recover with parchive.

    You'll still want actual backups on separate "media" to cover for the
    "whole disk failed" case.

    Of course. I always have backups. Of everything. Parchive is perhaps unecessary now that I have the photos on BTRFS with a mirror which can
    self correct but I still use it, as it can be useful if you accidently overwrite a file or delete one.
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