Re: Resuming mdadm reshape on a different system

[Jbum List <jbumslist@yahoo.com>]

> On Wednesday, December 4, 2024 at 04:26:22 PM PST, Roman Mamedov <rm@romanrm.net> wrote:
>
> On Thu, 5 Dec 2024 00:09:02 +0000 (UTC)
>
> Jbum List <jbumslist@yahoo.com> wrote:
>
>> My current situation:
>>
>> 1. Raspberry Pi 4 w/ 4 disk RAID 5 array
>> 2. PC for general development and test.
>>
>> I had a 5th disk I wanted to add to the array and in the interest of making things go faster, I decided to temporarily hook up the raid array to my PC.  I brought over the existing mdadm.conf settings from the Pi and the array was brought up successfully without any issue on my PC.
>>
>> I started the grow/reshape operation after adding the new disk and everything is going well.  However, I noticed that the rebuild speed isn't that much better than what I'm used to see on the Pi.  So rather than wait for the operation to complete (in a few days), I wanted to move the array over to the Pi and continue there.
>>
>> Can I pause/halt the reshape that's currently running on my PC and resume on the Pi?  I know you can pause/halt and resume on the same system it was started on but wasn't sure if that's possible across systems when both have the same configuration settings for the raid array.
>
> Should be no problem. The reshape state is not saved in the OS, it's on the
actual array drives.

Awesome.  That's music to my ears.  Thanks for the confirmation.

>
> Before moving it back, you could first try:
>
>  echo 1000000 > /sys/devices/virtual/block/mdX/md/sync_speed_min
>

I tried this but I didn't see any noticeable difference.  It could be due to other settings I had already tweaked (read ahead, stripe cache size, etc.).

> and see if this makes it faster.
>
> I would also expect the PC to be faster, at least if you connect the drives to
> its onboard fully independent SATA ports with enough PCIe bandwidth to the
> controller, and not e.g. the same USB enclosure.

My "PC" is really a laptop so I'm using the same multi-bay drive enclosure.  I suspect the USB interface is what's mostly limiting the speed.  Appreciate the suggestion though.

Thanks, Roman.