3ware raid controller 9750-4i

what do you mean by wrong unit number?

Within the raid 5 the other drives belong to u0 the failed drive belonged to u0. When replacing this drive it now is added to u1 not u0 .
When using tw_cli info c0 I see the drive with u~ after doing a tw_cli rescan it comes up as being in u1 not u0. This has never occurred before.
I tried running command  - tw_cli maint rebuild c0 u0 p1 however this errors so unable to change move p1 ot u0.
Below is output using tw_cli info c0
Unit  UnitType  Status         %RCmpl  %V/I/M  Stripe  Size(GB)  Cache  AVrfy
------------------------------------------------------------------------------
u0    RAID-5    DEGRADED       -       -       256K    5587.91   RiW    ON
u1    RAID-5    INOPERABLE     -       -       256K    5587.91   Ri     ON

VPort Status         Unit Size      Type  Phy Encl-Slot    Model
------------------------------------------------------------------------------
p0    OK             u0   2.73 TB   SATA  0   -            WDC WD30EFRX-68EUZN0
p1    OK             u1   2.73 TB   SATA  1   -            WDC WD3001FFSX-68JN
p2    OK             u0   2.73 TB   SATA  2   -            WDC WD3001FFSX-68JN

Thanks,
Michael

Can you not delete u1 via the CLI?

It is possibly an old drive with metadata on it that says it is part of an array, for all the controller knows you may be adding more drives from u1 later and want to keep that data.

Never have had a u1 unit. So not sure why that would show up. I can remove or delete from the CLI or the GUI application. Which is the better option?
Thanks.

Either will do. If the drive came from an old array and was U0 it would still have a separate config stored on it so would appear as a different U number than 0 as you already have 0.

Let me clarify. Drive designated P1 died and wasn't even seen by the raid controller anymore. I removed and replaced with a brand new drive same type, brand etc. It was seen, however not assigned to a unit. Had a u and  ~ symbol. Did a a maint rescan using tw_cli and the application added it to u1(The failed drive and the other drives belong to u0.) Have no idea why it would add it to u1.  I removed(Did not delete) it again and followed the same steps. Again it was added to u1. Seems no matter what I do it creates the drive in u1.  I guess I could try removing and running command "tw_cli maint rebuild c0 u0 p1 and hope it adds the drive to u0.
 Maybe it doesn't like the hot swap. Perhaps I should cold swap. Any ideas are appreciated.

Odd that it was brand new, normally this kind of things is with second hand drives. Should still be able to add it to U0 if you delete U1 first though without removing the drive physically.

Hmm. Will see what happens.

Once deleted what is the recommended command to add back to c0 u1? I'm thinking tw_cli maint rebuild c0 u0 p2.
I'm quite sure if I run the w_cli maint rescan command it will add as a u1.
Thanks,
Michael

If I'm quite sure about something without even trying it I normally take a backup and then try it anyway. It's how I learn.

Yeah that is what I do. However the backup will be huge.

Replacement drive finally loaded in u0 however irregardless of the new drives I use after starting to rebuild it changes to ecc error. See below.
How do I get around this?
Thanks.
Unit  UnitType  Status         %RCmpl  %V/I/M  Stripe  Size(GB)  Cache  AVrfy
------------------------------------------------------------------------------
u0    RAID-5    DEGRADED       -       -       256K    5587.91   RiW    ON

VPort Status         Unit Size      Type  Phy Encl-Slot    Model
------------------------------------------------------------------------------
p0    OK             u0   2.73 TB   SATA  0   -            WDC WD30EFRX-68EUZN0
p2    OK             u0   2.73 TB   SATA  2   -            WDC WD3001FFSX-68JN
p3    ECC-ERROR      u0   2.73 TB   SATA  1   -            WDC WD3001FFSX-68JN

You said "tw_cli maint rebuild c0 u0 p2" that implies that you replaced p2, If that assumption is correct it's just another disk in the array that's a bit unhealthy. It may struggle to rebuild if that is the case.

What you do not see is that Port 3 is physical p1(sata 1). So for whatever reason it has issues when trying to rebuild after adding p1 to u0.
 So this is still the same port same drive etc. Nothing has changed relative to p1 having issues being rebuilt.Below is a snippet from 3DM2 utility
0       WDC WD30EFRX-68EUZN0       2.73 TB       SATA       0       --       0       OK       
2       WDC WD3001FFSX-68JNUN0       2.73 TB       SATA       2       --       0       OK       
3       WDC WD3001FFSX-68JNUN0       2.73 TB       SATA       1       --       0       ECC ERROR

In that case it suggests to me that the replacement may be dodgy although it may be poor controller error handling.

Do you think the controller could be replaced without issues or perhaps it is a firmware issue. There is an update available.
Thanks,