When will software RAID hotswap work?

[To-M]

Thanks for the research - I will forward to our engineers. Hopefully we can do this. Please give us time as we are booked with request.

[Robotbeat]

You're welcome, Todd.

Heh, no dice. I have 3 drives plugged in, which DSS sees. If I unplug one of them and do a system rescan, for some reason it only sees ONE drive (the middle one, if you're curious). If I reboot so that I only have two drives and then plug the third one in and do a rescan, for some reason it still only sees ONE drive (oddly). So, I guess I would highly recommend only plugging in and unplugging drives once the system is OFF if you're using the software RAID.

Someday, though...

(Robust software raid support would be great so that someday I can combine lots of iscsi volumes into one big volume using the iscsi initiator built-in to DSS. There are probably better ways to do this, though.)

[Robotbeat]

I meant "unit rescan," not "system rescan."

[Robotbeat]

After looking at this again, I realized that I hadn't set the BIOS to set up the sata drives as AHCI. I think they were set up to look like IDE drives or something like that. Anyways, AHCI supports hotswap, whereas regular IDE drives do not, so there's still a good chance that hotplugging could work once I set the BIOS properly on Monday.

[Robotbeat]

Alright! Well, after switching to AHCI mode in the BIOS settings, hotswap seems to work. When I have 3 drives, pull one out and do a unit rescan, only two drives show up. When I put it back in and do a unit rescan, three show up! Now, I haven't tried this with a software raid, but it seems this should work, now!

This will be great if it works, since we won't have to spend money for a hardware RAID controller on the smaller boxes.

[To-M]

Thanks for the update on this - keep in mind that we don't have the expansion capabilities like the HW RAID does. Though we are working to have this but I have no ETA as to when.

Let me know this works with the RAID setup, I would like to pass this around to others.

[Robotbeat]

I have made a RAID 5 array with 3 drives (2+1).

If I click Setup->S/W RAID->MD0, I'm given options to select an array member as faulty. There's also a place to mark a unit for removal, but it is greyed out. Perhaps I need to mark it as faulty first? This is what the help UI says:

Function: Manager

Using this function you can manage the RAID array.

Available operations:
RAID 0:

The design of this RAID does not permit management of it. No units can have failed status. If any of them fail, the whole array will be disabled.

RAID 1:

* To mark a unit as Faulty, check the appropriate option (in the F column) and click Apply.
* To delete any unit from an array, check the appropriate option (in the R column) and click Remove.

RAID 5:

* To mark a unit as Faulty, check the appropriate option (in the F column) and click Apply.
* To delete any unit from an array, check the appropriate option (in the R column) and click Remove.

RAID 6:

* To mark a unit as Faulty, check the appropriate option (in the F column) and click Apply.
* To delete any unit from an array, check the appropriate option (in the R column) and click Remove.

RAID notation:

* PR - priority in array This represents the priority of a spare unit which will be added to the array if another unit is marked as Faulty. The higher the priority, the sooner this unit will be used.
* F - faulty The unit can be removed from the array.
* R - hot remove This unit can be removed from the array without shutting down the system.
* ST - characterizes the state of a unit in the array, which can be:

* A - active
* * - unit number within the array
* S - spare or spare rebuilding This means that the unit is free and can be added to an array, or is free and is currently rebuilding.

Limitations:

* It is not possible to set any unit as Faulty, if the matrix is degraded or during resync/rebuild.
* When using RAID 1 and RAID 5, it is possible to mark only one disk from among the active disks as faulty. This regulation is not valid for spare units in an array.

Note
Only one disk from within the active group in an array can be marked as Faulty or Removed.

Location
SETUP -> S/W RAID -> UnitMD[#] -> Function: Manager.

I am going to try to do this manual remove method first, while accessing files stored on an iscsi volume on this array. I'll let you know what happens and if I can rebuild it without rebooting!

[Robotbeat]

It works!

Before just tearing the drive out of there, I manually selected the unit as "F--faulty" in the s/w raid manager. This caused the raid to become degraded. Then, I selected the unit as "R--hot remove". After this, I physically removed it. Nothing bad happened! Throughout this whole process, I had been playing a long audio file stored on an iscsi volume on this raid array. I did a unit rescan and found that, indeed, the drive was no longer there, but the other two were still there, and the array was fine. It was just degraded but still clean.

Then, I put the drive back in the slot and did a unit rescan. It showed up as "available"! So, I added it as a spare for MD0, which was in a degraded state. It immediately started rebuilding. Rebuilding is faster than initially building, for some reason (50MB/s vs. 20-40MB/s).

So, I'm still listening to the same audio file that I was at the beginning at this process without any hiccups or errors.

Tomorrow, I'm going to just remove the drive immediately without warning the software. We'll see how that goes!!!