4 ms·

The amount and type of work that would be required to take a 6disk to a 7disk (in place) is quite hard. If you can take some downtime, you'd really want to snap

The amount and type of work that would be required to take a 6disk to a 7disk (in place) is quite hard. If you can take some downtime, you'd really want to snap, send to a new larger system, go down, do the final copy, and come back up. That or work with more vdevs, but then you might have unevenly striped data. And there are filesystems that are expandable and meet your other requirements, they just aren't cheap. IBM GPFS is one I work with regularly.

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 ago
  It's the checksumming, striping, and parity, especially in context of CoW snapshots that complicate this operation.
  - mappu 10y ago
    LVM2 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 ago
      RAID 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.

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 ago
It's the checksumming, striping, and parity, especially in context of CoW snapshots that complicate this operation.
- mappu 10y ago
  LVM2 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 ago
    RAID 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.