Swapping in good disk for bad disk

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Swapping in good disk for bad disk

Postby Sharko » Tue Sep 20, 2016 8:26 pm

Hi, me again. I have four disks in my Mac Pro 5,1; three were brand new 2TB Toshibas, and one was a little-used 2TB HGST backup disk from an external enclosure. It's set up as two mirrored VDEVs of 2TB each, total of 4TB in the pool. The HGST is now showing signs of failure: reallocating sectors, pending count, etc. I ran a long SMART self test on the HGST, and it failed. So, I need to get it out of there and sent off under RMA, and slot in a replacement.

I've got a brand new 4TB disk that was going to be a backup for the whole array. After several misadventures in El Capitan, I finally got it formatted and partitioned in Snow Leopard's Disk Utility (no joke, the recent versions of Disk Utility are crap).

I wanted to run my strategy by the gurus here, and see if you think it is workable.

1. Connect the new 4TB disk to the computer via USB 3 using a Newertech Universal drive adapter, since all the SATA brackets are currently filled in the Mac Pro.
2. Use 'gpt' to format the 4TB such that it has my usual size ZFS partition.
3. Do a zpool 'attach' to attach the new disk to the failing VDEV, making it twice redundant (three disks mirrored to each other).
4. Wait for the resilver to complete on the new disk (accessed via USB3).
5. Once complete, perform a 'detach' on the failing drive to remove it from the VDEV.
6. Power down the computer, remove the failing drive from the SATA bracket, and put the new drive in its place.
7. Power up, import, ready to run.

The only step I'm a little unsure about is step 6; will ZFS be ok with recognizing a drive that used to be on the USB interface, and now seeing it on the internal SATA interface? I could leave it on the USB interface until the replacement drive comes back, but I'd prefer to get it all buttoned up inside for the few weeks that the RMA process is going to take.

Thanks for your advice,

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Joined: Thu May 12, 2016 12:19 pm

Re: Swapping in good disk for bad disk

Postby Brendon » Wed Sep 21, 2016 12:19 am


You should just replace the disk in place. There is a risk that the apparent sector size wlll be different on USB vs SATA, rendering the disk unreadable once installed in the computers internal drive tray.


- Brendon
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Joined: Thu Mar 06, 2014 12:51 pm

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