[OpenIndiana-discuss] Intruducing a new pair of rpool mirror discs

[Coalson, Timothy Scott (S&T-Student)]

Having (much) less than 300GB of data doesn't mean none of it is written past the 300GB mark, and I believe mirror vdevs use the same offset in each component device for the mirror copies.  Even for relatively simple fs-on-softraid setups, you have to use specialized tools to move data out of the end of the partition and update its new location in all other filesystem structures, and these usually operate while the filesystem is unmounted.  I don't know if such tools exist for zfs.  Doing this with the filesystem mounted would need at least block pointer rewrite (which has been on the wishlist for a long time).  I expect zpool will just tell you it can't be attached as a mirror because it is the wrong size, no matter what other options used (take care not to accidentally use "add").

However, if you made a new pool from scratch and used zfs send and receive, and then did whatever to get the bootloader squared away, you could then swap to the new disks.

SSDs would be a lot more noticeable upgrade than velociraptors, and run cooler.  I haven't tried setting up overprovisioning on zfs boot drives yet, though.

Tim

________________________________
From: Harry Putnam <reader at newsguy.com>
Sent: Thursday, October 15, 2020 7:49 PM
To: openindiana-discuss at openindiana.org <openindiana-discuss at openindiana.org>
Subject: [OpenIndiana-discuss] Intruducing a new pair of rpool mirror discs

I've been running on a single rpool disk of what was a mirrored pair for
some time and am planning on correcting that now.  One disc went belly
up some months ago.

I want to take the opportunity to introduce a pair of 300gb
velocaraptors (sp) to replace both the bad disk and the working disk.

'the orginals where a pair of 700GB sata discs now quite long in the
tooth, and as mentioned one down already.

So, I'm wondering how to go at this.  If I  stick in one of the
300 GB `raptors' and make it a mirror to the working 700gb rpool disk what
will happen?

There is nowhere near 300GB data on that single 700GB disk holding
rpool.

Will that mean that the mismatch in disk space will just be lost from
the 700GB disk?  And once I've made the new 300gb mirror bootable,
could I then pull that last remaining 700GB disk and insert the second
300gb `raptor, make it a mirror, render it bootable and proceed on my
way with once again a matched pair of mirror discs on rpool?

Somehow I have bad feeling I'm overlooking a few things that might
bite me in the booty.


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