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Mdadm (Linux's built-in software RAID) can expand a RAID array online, and has been able to do so for about a decade. It's not fundamentally that complex of an
by teraflop 10y ago
Mdadm (Linux's built-in software RAID) can expand a RAID array online, and has been able to do so for about a decade.
It's not fundamentally that complex of an operation, but there are enough details to be careful of that I don't see why it makes sense to reimplement it in every filesystem.
- Terribledactyl 10y agoIt's the checksumming, striping, and parity, especially in context of CoW snapshots that complicate this operation.
- mappu 10y agoLVM2 is a filesystem-agnostic layer that gives you CoW snapshots on top of mdadm's striping/parity. From your list, that just leaves checksumming for bitrot, which you can do at the RAID level via mdadm check, or at the filesystem level with sha1sum --tag / sha1sum -c (although maybe that's not as nice as ZFS/btrfs).
- Annatar 10y agoRAID controllers cannot be relied upon to do check sums, as most RAID controllers do not possess this capability, and of those which do, their firmware is opaque and buggy, and therefore cannot be trusted. If you care about your data, never use hardware RAID, and always use ZFS or Oracle ASM. mdadm(8) is a good start on GNU/Linux if one is forced to run on an (older) operating system version with only ext3 or XFS, however while it provides administration consistency and scales to many systems, it does not provide data checksumming, and therefore no data corruption detection and no self healing capabilities like Oracle ASM or like (Open)ZFS.