Before we get into this, two things:
I'd parse the array device members from /proc/mdstat unless there's
something easiler to parse.
I'd parse the location of drives-by-partition-id from "lsblk -bfr". That
shows mount points too.
So that lets you figure out:
lsblk: mount-point -> mounted device (an md device in this case)
mdstat: md device -> sdXn names of its partition components
sdXm: -> sdX the physical device you want to spin down
for the current state of the system. From the below it sounds like the
mdstat step isn't correct.
On 05Jun2020 22:30, Patrick O'Callaghan <pocallag...@gmail.com> wrote:
That doesn't seem to be what's happening:
1) Starting from a fresh reboot, with the array unmounted but active
according to mdadm, I make it inactive:
# echo inactive > /sys/block/md127/md/array_state
(At this point I can make it active again using "echo active ...")
I presume that that just idles the md device; not changing its members.
In particular, it still believes that sda1 and sdb1 (to invent some
device names) are its members.
Check /proc/mdstat to be sure.
In fact, look at /proc/mdstat after every md change; you'll find out
what the md system thinks this way.
2) I now delete the component drives:
# echo 1 > /sys/block/sdd/device/delete
# echo 1 > /sys/block/sde/device/delete
After a timeout, the drives spin down. So far so good.
I think you should remove the md device before you do this. At least
"mdadm --stop". See what /proc/mdstat says after doing that.
I'd be concerned that md would treat device deletion like drive failure.
Deconfigure the md device first.
3) To spin them up again, I do:
# echo "- - -" > /sys/class/scsi_host/host6/scan
They come up with different numbers (/dev/sd[fg])
However the md system does not detect them:
The md system probably doesn't even know they need detecting, because it
still has the old spec.
# mdadm -A
mdadm: an md device must be given in this mode
You probably want --auto-detect instead. -A is for manually constructing
the array.
It's very possible (indeed likely) that I'm stopping the array in the
wrong way, but I don't see any other way to do it. The mdadm man page
mentions '-A' as the way to start an array, but doesn't talk about how
to stop it, so it could just be leaving out-of-date status information
around and that's what's confusing it.
Looks like --stop should delete/deconfigure the array. --auto-detect
should find unconfigured array members and make new md devices from
them.
Cheers,
Cameron Simpson <c...@cskk.id.au>
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