How to downgrade parity drive size?

[abq-pete]

I've decided to downgrade my current 1.5TB parity to 1.0TB.  All my data drives are 1.0TB.  However, when I try to assign the 1.0TB, I get a message indicating that the drive needs to be the same size or larger.  I was expecting the array to recognize that the largest data drive is 1.oTB so using a 1.0TB parity drive would be sufficient.  Any ideas?

 

Thanks and regards,  Peter

[NLS]

Check exactly how many bytes are reported.

 

Some times a few bad sectors, a different brand or even a different build (!) can result in slightly different numbers.

You don't want your parity to be even one byte less than the rest.

 

If this is the case, you can still do it.

Add back your 1.5, let it fix parity again, see which drive is REALLY the biggest (in exact bytes) and remove it.

Add your other 1TB drive (attempted parity) and assign it in place of this drive - let the parity build it again.

Now you can again remove the 1.5TB parity and you can put your really "biggest 1TB" drive in its place.

 

 

[SSD]

All drives 500G+ have a standard size.  All manufacturers match exactly.  Bad sectors won't influence the size (they are remapped via S.M.A.R.T.). There was an issue of some motherboards reserving a few sectors at the front of the disk that I kind of remember.  There was a fix I believe.

 

I'll see if I can find the thread.

[abq-pete]

NLS,

 

The main screen shows all drives having the same size at 976,762,552.  In the syslog, I see that all drives have 1953525168 512-byte hardware sectors (1000205 MB).  Is there another way to see the info?

 

bjp999,

 

I have an Intel D975XBX2 that uses the 975x northbridge and ICH7R southbridge.

 

Thanks to both of you for taking the time to respond.

 

Regards,  Peter

[SSD]

1.  Did you press the "restore" button to get it to build parity onto the new parity disk?

 

2.  or did you just try and replace the parity disk with the new (smaller) parity disk?

 

You'd have to do #1.  If you tried to do #2 it would likely tell you it could not restore the parity disk (a 1.5T disk) onto a 1.0T disk.

 

Note that pressing the restore button is usually a bad idea, as it causes your parity information to be lost. After pressing it, any chance of recovering a broken or damaged disk is lost.  But since you are replacing your parity disk, this doesn't really apply. 

 

Before doing #1, I'd recommend a full parity check with the 1.5T parity drive in place to make sure all you your drives are fully readable.  It may be a bit tricky to get back to that configuration.  You'd likely have to do the "trust my parity" process described in the FAQ.

 

Here are links to the threads I was thinking about.   I don't think this applies but check them out to be sure.

 

http://lime-technology.com/forum/index.php?topic=2230.0

 

and

 

http://lime-technology.com/forum/index.php?topic=2444.15

 

[abq-pete]

I attempted #2 but was stopped because of the messages.  I've done several parity checks in the past few weeks as I've been checking out new hardware so I am pretty sure the data drives are fine.

 

Thanks for the links.  I've read them before but as you said, they don't seem to apply.  I will go ahead and start the restore process.

 

Thanks and regards,  Peter

[abq-pete]

bjp999,

 

I clicked the "I am sure I want to do this" followed by the restore button.  Now all drives are marked blue (including the new parity drive).  I have two choices now:  Start or Restore.  Do I just go ahead and click start then?

 

Regards,  Peter

[SSD]

Yes -

 

Pressing restore puts you back in a state before you started your array for the first time.  You may not remember, but when you first loaded unraid and assigned disks to slots on the device page, they were BLUE.

 

The second you press the start button, unRAID will save your drive configuration in a file called "super.dat".  The disks will never be blue again (unless you press restore again).

 

Just make sure the right disk is in the parity slot, then press start.  Your array will start and parity will begin to be constructed.

[abq-pete]

I have to admit, it was a little unnerving to follow the process but it is running right now.  I now understand the process and really HATE the name of that button!  Thanks again for all the help.

 

Regards,  Peter

[SSD]

I have to admit, it was a little unnerving to follow the process but it is running right now.  I now understand the process and really HATE the name of that button!  Thanks again for all the help.

 

Regards,  Peter

 

We all do.  Although a bit unnerving, perhaps, you are not at any greater risk rebuilding parity as you would have been replacing the parity disk with another parity disk as you originally attempted to do.

 

unRAID will never let you replace a larger disk with a smaller one.  Had you wanted to downsize a data disk it would have been harder.

[RobJ]

Added to the FAQ (with link back), here.  Feel free to edit or expand.