> > This is in fact one of the very few places where Hardware RAID solutions can have an edge over Software solutions - if you use a hardware RAID card, the extra write copies of the data will not have to go over the PCI bus, since it is the RAID controller that will generate the extra copy.

This is not a thing to bother (especially after we moved from PCI to PCI-E) for a home user.

The only great thing about HW RAID is what in case your primary drive fail-but-not-fail-completely, ie it would still be seen in the BIOS and BIOS would try to boot from it (but it wouldn't be able to, because drive is half-dead) is what for the BIOS a controller presents a single device and so it would allow booting from a healthy drive.

But again, if this is not a server in a remote oil digging site served twice a year by air (been there, done that) this is not a thing to bother for a home user.

> the possibility of the hardware controller failing is a worry, so I’d need to have a backup strategy for the backup disks

If you use a basic mirror (striped or not) the recovery process is straightforward - for a simple mirror just stick it in any other system/controller, for a striped you would need GetDataBack or R-Studio or just find a newer model of the RAID card from the same vendor.

In your case I would advise to have a single disk in the ODD bay as a boot/system drive and use both your HDDs as an LVM PVs, without fdisk shenanigans. If you/when you decide to upgrade/replace disks the migration would be just a couple of commands like

    pvcreate /dev/sdc
    vgextend your_vg /dev/sdc
    pvmove /dev/mapper/your_vg__your_lv /dev/sda /dev/sdc
    vgreduce /dev/sda

Wow! That's all really informative. I had thought that a non-striped, mirrored disk should be usable if the H/W RAID controller failed (given that all the data is stored on the disk) but I didn’t know for sure. I didn’t think it would also be possible to recover striped disks.

Thanks for the great advice on using LVM and the commands for replacing a disk. I only recently cane across a system that used the disk block device itself as a physical volume – rather than partitioning it via fdisk or parted. Other than using LVM for creating snapshots, I haven't really used it for anything interesting.

> but I didn’t know for sure

The array metadata is just stored at the end of the disk, so this is not a problem to just attach a disk somewhere rlse

> commands for replacing a disk

Take it with a grain of salt, I just wrote them from memory. But the overall process is exactly as I said.

Glad you found that helpful.

Funny, I have the identical setup with a small SSD for /, and two of the 3TB Reds for my media/music/files. I have seen enough pain from HW Raid controller setups (custom drivers, configs, long recovery) that HW Raid was right out. Then, for soft raid I had bad experiences in the past where the system refused to come up with one disk in the mirror pair bad. I'm sure there is a way to configure this properly but at this point I said fuck it and just mirror one of the WDs by hand to the other via rsync. Think hard (or even test): what actions will need to happen when one of your disks fails? And second, do you need backup or RAID more? Fat-finger deleting a file on a RAID-backed file system will leave you with no backup unless it has snapshots.

Some notes.

- Not having Raid really doesn't matter. The primary purpose seems to be to save a little bit of space by clever checksumming or increase read performance from parallel operation, but none of this is valuable to me.

- I use ext4. I think it would make sense to move to a snapshot-capable system to make the periodic rsync-backups more correct (I don't even bother dropping to r/o mode, since it's fairly static data).

- What really keeps me up at night: bit flips silently corrupting files. I think btrfs or ZFS are supposed to solve this through constant background checksumming. I really need a periodic process to checksum every file and take action on exceptions. Note that RAID will not help you with this.

- This has worked pretty well so far. Twice already (over 12 years) have I had one disk in the pair fail, upon which time I would order a new pair (they were bigger/cheaper by that point and I figured the other one would fail soon) and rebuild the server.

Thanks so much for sharing your experience. I look after a couple of server in my current job that have hardware RAID (Dell) but they were set up by my predecessors and they’ve never given any trouble since I started working there (touch wood). I have also not had any problems with Linux Software RAID, e.g., I was pleasantly surprised to discover that I could move the RAID 1 disks from my previous home server (a repurposed Dell workstation) to the Proliant microserver and my Debian OS had no problem recognising them.

The consensus seems to be that RAID isn’t particularly useful for a home server. Backup would be more useful as I would be more likely to accidentally delete or over-write a file than for a disk to fail catastrophically) so I think I might use the second disk, similar to how you use yours. I would also be better served by using ZFS; its de-duplication would also be useful – so I’m going to try it as an experiment.

> according to the Linux Raid Wiki¹, Hardware RAID 1 is better than Software RAID 1.

Don't take that too much into consideration - the article was last updated in 2007 ( https://raid.wiki.kernel.org/index.php?title=Overview&action... ) so it lacks some details (the same can be said as well for many ZFS-related infos that you might find) => nowadays doublechecking articles related to raid and ZFS is a must.

In my case I bought some HBA (Host Bus Adapter) cards (e.g. LSI SAS 9211-8i), set their BIOS to not do anything special with the HDDs connected to it (to be able to use them as well with other controllers) and used mdadm (earlier) or ZFS (now) to create my RAIDs => it works well, i get max throughput of ~200MiB per disk, I have all fancy features of ZFS without the problem of proprietary stuff related to the controller card :)

Thanks for the tips and feedback. I’ll stick with Software RAID. I wasn’t sure that the system would have enough resources to support ZFS but I think I’ll try it out before I commit large amounts of data to it.