If I were to run ZFS on my laptop with a single disk and copies=1, and a file becomes corrupted, can I recover it (partially)?
My assumption is the read will fail and the error logged but there is no redundancy so it will stay unreadable.
Will ZFS attempt to read the file again, in case the error is transient? If not, can I make ZFS retry reading? Can I "unlock" the file and read it even though it is corrupted, or get a copy of the file? If I restore the file from backup, can ZFS make sure the backup is good using the checksum it expects the file to have?
Single disk users seem to be unusual so it's not obvious how to do this, all documentation assumes a highly available installation rather than laptop, but I think there's value in ZFS even with a single disk - if only I understood exactly how it fails and how to scavenge for pieces when it does.
It depends. Metadata is always redundant with 2 copies (even when using copies=1). So if the file's metadata is corrupted, yes ZFS will fully recover and rewrite a 2nd good copy of the metadata. But if the data is corrupted, then ZFS can do nothing to recover (you may be able to partially read the file, but the rest of it will return I/O errors.)
Ok, so zfs for single drive users doesn't fix single data corruption.
Definitely I'm going to use my solution so. All the next generation FS stuff is cool (btrfs also indeed) but for the simplest use case people just need safe data and fix it it the disk goes bad.
My assumption is the read will fail and the error logged but there is no redundancy so it will stay unreadable.
Will ZFS attempt to read the file again, in case the error is transient? If not, can I make ZFS retry reading? Can I "unlock" the file and read it even though it is corrupted, or get a copy of the file? If I restore the file from backup, can ZFS make sure the backup is good using the checksum it expects the file to have?
Single disk users seem to be unusual so it's not obvious how to do this, all documentation assumes a highly available installation rather than laptop, but I think there's value in ZFS even with a single disk - if only I understood exactly how it fails and how to scavenge for pieces when it does.