ReadyNAS 6 - Raid 5 Drive Replacement

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haspden wrote:

If 1 drive fails, will the system to continue to work (obviously without redundancy at this point... Can I swap it out & replace the drive with a new blank one? I assume that, I can "hotswap" the drive & the NAS will resync the data to the new drive and re-establish the Raid Redundancy,

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The system will continue to work, and you can hot-swap the replacement drive.

Note that this doesn't mean your data is safe.  If a second disk fails during the resync (which does happen), your data will be lost.  Also there are lots of other failure modes (and of course theft, fire, etc) that can result in data loss.  The only way to keep your data safe is to back it up.  Ideally your backup plan would consider disaster recovery (including ransomware).

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haspden wrote:

Would X-Raid would be more suited to wanting to increase storage space with incremental increases as each drive is upgraded?

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Yes.  You can also expand with flexraid, but it is more complicated (as you need to create and manage RAID groups yourself).

With XRAID, the capacity rule is "sum the disks and subtract the largest".  For instance, 2*3TB + 2*1TB would give you a volume size of 5 TB (about 4.55 TiB).  4x1TB would give you  3 TB of space - your comment on that is incorrect.

You are correct in thinking that you'd need two 3 TB drives to get any expansion.  That is required to maintain redundancy.  Likely you will need to reboot after you resynce the second 3 TB drive in order to trigger the first expansion.  After that, no reboot is needed.

Converting to XRAID is easy.  Go to the volume tab in the web UI.  If there is a green stripe on the XRAID control (on the right) then XRAID is already enabled.  If there is no green stripe, then just click on that control.

FWIW, it is often more cost-effective in the long run if you use larger drives.  You might consider going with 4 TB drives instead of 3 TB.

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haspden wrote:

in X-Raid how does it handle drive failure?

It handles drive failures identically to flexraid.  As noted above, XRAID just hides the complexity of managing RAID groups yourself. 

XRAID uses multiple RAID groups to achieve vertical expansion.  To give an example, let's take your 2x3TB+2x1TB case.

If you start with 4x1TB you only have one RAID group in the volume, and that is RAID-5.

Once you've expanded to 2x3TB+2x1TB, the system still has that RAID group.  It also creates a second RAID group to use the remaining space. That would be 2x2TB RAID-1.  Both groups have single redundancy.  The two groups are joined, so there is only volume (and one file system).  Files will be spread across both groups - as far as the file system is concerned, there is one virtual disk.

If disk 2 were to fail, then when you replace it the contents are reconstructed from the remaining disks.  This is done separately for each RAID group.  The 4x1TB group is rebuilt using RAID parity blocks (normal RAID-5 stuff).  The 2x2TB group is mirrored, so the data is just copied from disk 1 (normal RAID-1 stuff).

Also, if you upgrade disk 3 to 3 TB, the first RAID group is just reconstructed.  The second RAID group is expanded to 3x2TB (converted from RAID-1 to RAID-5).  You still see a single volume, with 7 TB ( about 6.37 TiB) of space.