On Mon, Apr 27, 2015 at 09:24:47AM +1000, Noah O'Donoghue wrote:
Don't forget the other benefit of hardware raid is being able to boot from a degraded array.
it's an advantage of software raid too. i've been doing that from software raid for years. in fact, it's one of the reasons i usually have a RAID-1 /boot partition no matter how the rest of the drive space is being used (RAID, ZFS, btrfs, whatever) that flexibility is one of the benefits of software raid - i can decide on a per-partition basis (rather than per-disk) what kind, if any, of RAID i'm going to have. e.g. my current main system has a matched pair of 256GB SSDs - using RAID-1 for / and /boot, and no raid for the swap, ZIL, and L2ARC partitions (RAID makes no sense for those). the bulk data storage is on two 4x1GB ZFS RAID-Z1 pools (mounted as /export and /backup - the latter takes rsync and 'zfs send' backups from all systems on my home network). this wouldn't be possible on hardware raid. (i haven't upgraded the RAID-Z pools to larger/newer drives because the current capacity is adequate for my needs and i'm holding out for SSDs to get *much* cheaper. with luck, the current drives will last until 1 or 2 TB SSDs are affordable to buy in quantities of 4+, or for 4+TB SSDs to be affordable in pairs)
EG if you use software raid and your grub is on a failed drive, you will have to manually force the BIOS to boot from the other (working) drive or it will just hang on boot.
this might be a problem on ancient hardware, but it's not a problem on anything reasonably modern (for at least the last 5+ years)
For this reason it's worth considering having at least your grub loader on a RAID partition that uses the hardware RAID controller, even if the rest of your drives use software RAID. Or being aware of this limitation, and being prepared to manually boot or boot grub from an external device if your raid is degraded.
or just grub-install to all drives and configure the bios to attempt to boot from each drive in turn. i haven't seen a BIOS (incl. UEFI) for years that doesn't allow you to specify a boot order. craig -- craig sanders <cas@taz.net.au>