HDD to SSD "the disc must be as big or bigger than the original" Error

[tomorrowsman]

I've been using unRaid since 2012 and have swapped out countless drives over that time.  My 4TB WD HDD hard drive is on the way out, so I decided to replace it with a new Crucial MX500 SSD, others of which I've had in my array for years.  For some reason I'm getting an error that "the disc must be as big or bigger than the original" even though both are 4TB.

Is there any way to have my unRaid OS work through this?  In all these years and swaps I've never encountered this before.

[itimpi]

The problem will be that Unraid uses a different start sector for HDD and SSD (for performance reasons) so the SSD will have a few less sectors available for data than the HDD had.

 

The only easy way around this that I can think off is to use the New Config tool to get the SSD into the array, rebuild parity, format the SSD, and then mount the old HDD drive via Unassigned Devices to copy its data back to the array.  This would not be ideal as if the HDD failed during this process (and you do not have a backup of its contents) you could end up with data loss.

[tomorrowsman]

Yikes, that sounds scary...so I'm not missing anything, is it:

1. Shut down array.
2. Remove HDD, add SSD, reboot array.
3. Add SSD to array via New Config tool.
4. Rebuild Parity - I'm not technical so forgive me, but why wouldn't parity write to the new SSD at this time?  I think this is the part of how parity works that confuses me the most; can't the array see the SSD as a new drive replacing a dead drive and use parity plus the other drives to rebuild?  Or is this where the start sector issue becomes the issue?
5. Format the SSD - I assume in the dashboard?
6.  Mount HDD to the array via Unassigned Devices - though if I'm already at my max SATAs I'm blocked here...
7. Copy data back, meaning, rebuild the array again?
8.  Shut down, remove HDD, reboot?

 

[trurl]

SSDs in the parity array cannot be trimmed.

[tomorrowsman]

2 minutes ago, trurl said:

SSDs in the parity array cannot be trimmed.

Apologies, I do not know what that means.  Did I refer to that in one of my steps?

[trurl]

18 minutes ago, tomorrowsman said:

Apologies, I do not know what that means.  Did I refer to that in one of my steps?

No you didn't mention it. I just thought you might be unaware of this limitation. Apparently so.

 

https://www.google.com/search?q=why+trim+ssds

 

This is not allowed in the parity array since it might invalidate parity.

[trurl]

52 minutes ago, tomorrowsman said:

Rebuild Parity - I'm not technical so forgive me, but why wouldn't parity write to the new SSD at this time?

Rebuilding parity doesn't write to anything except the parity disk.

[trurl]

53 minutes ago, tomorrowsman said:

 Mount HDD to the array via Unassigned Devices

Not really "to the array". That is why it's an Unassigned Device.

[trurl]

54 minutes ago, tomorrowsman said:

Copy data back, meaning, rebuild the array again?

No, just means copy. The Unassigned Device isn't part of the array. At this point the SSD in the array is empty. You just need to copy the data back to it from the Unassigned Device.

 

[trurl]

56 minutes ago, tomorrowsman said:

Format the SSD - I assume in the dashboard?

Main - Array Operation.

 

Make sure the only disk listed for formatting is the new SSD.

[trurl]

41 minutes ago, trurl said:

SSDs in the parity array cannot be trimmed.

Also, SSDs in the parity array can only be written at parity speed.

 

Both of these limitations are why SSDs are not usually put in the array. You have discovered another with your current problem.

[tomorrowsman]

46 minutes ago, trurl said:

No, just means copy. The Unassigned Device isn't part of the array. At this point the SSD in the array is empty. You just need to copy the data back to it from the Unassigned Device.

 

So I remove the HDD from the array, add the SSD to the array, mount the HDD as a UD, then copy to the SSD?

[tomorrowsman]

At the absolute most raw level, couldn't I add the SSD to the array, rebuild parity, then remove the HDD and rebuild parity again, with no data loss?  I know that is a super ham-handed way to approach the problem, but wouldn't it work, given none of the drives are greater than half the size of my parity drive?

 

I'm asking about alternatives because I do not see any "Copy" function in any of the menus that would enable me to copy the HDD to the SSD, so I'm guessing it's something above my very low level of expertise.

Edited May 3 by tomorrowsman

[JorgeB]

13 hours ago, tomorrowsman said:

At the absolute most raw level, couldn't I add the SSD to the array, rebuild parity, then remove the HDD and rebuild parity again, with no data loss?  I know that is a super ham-handed way to approach the problem, but wouldn't it work, given none of the drives are greater than half the size of my parity drive?

 

You can, but you would still need to copy the data from one disk to another, and it will be much slower because of parity, and it's also important to know what this means:

 

16 hours ago, tomorrowsman said:

My 4TB WD HDD hard drive is on the way out

Please post the diagnostics first so we can see SMART for that disk, that makes it easier to give advice.
 

[tomorrowsman]

Thank you everyone for your help; I will start a new thread with I think a much simpler question!