auto assemble in read-only mode?

Discussion:

Errol Neal

2014-10-06 13:06:35 UTC

hi folks. is it possible to assemble an md device in read-only mode?
after an array has been assembled, I know I can mark it as readonly with --misc -o /dev/md0 for example, but only after its been assembled it seems..

tia,
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Errol Neal

2014-10-07 06:56:31 UTC

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Post by Errol Neal
hi folks. is it possible to assemble an md device in read-only mode?
after an array has been assembled, I know I can mark it as readonly with --misc -o /dev/md0 for example, but only after its been assembled it seems..

Hi again. No thoughts here?
I'm need to run a RAID1 device on two independent nodes (shared storage) and I'd like to assemble the device on the "slave" node in read-only mode to prevent any sync actions and etc.
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NeilBrown

2014-10-07 07:15:20 UTC

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Post by Errol Neal

Hi again. No thoughts here?

Not even 18 hours since you last asked - what do you thing this is? The
Internet :-)

Post by Errol Neal
I'm need to run a RAID1 device on two independent nodes (shared storage) and I'd like to assemble the device on the "slave" node in read-only mode to prevent any sync actions and etc.

Did you try adding the "--readonly" option to your --assemble command?
(Always best to report everything you tried and how it failed - requires less
guess work).

I hope you don't expect too much of a filesystem mounted from such an array
while the other node is writing to the array...

NeilBrown

Post by Errol Neal
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Errol Neal

2014-10-07 12:31:34 UTC

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Post by NeilBrown

Post by Errol Neal

Hi again. No thoughts here?

Not even 18 hours since you last asked - what do you thing this is? The
Internet :-)

HAHA. I tend to feel ignored on large mailing lists lol. Need to see my therapist again ;)

Post by NeilBrown

Did you try adding the "--readonly" option to your --assemble command?
(Always best to report everything you tried and how it failed - requires less
guess work).

I did that previously and mdadm told me that "option --readonly not valid in assemble mode". E.g. "mdadm --assemble --scan --readonly".
The readonly flag seems like it can only be used after a device has been assembled. So for example, after the device has been assembled, I can
run mdadm --misc -o /dev/md0 but that is not always safe for my use case.

Post by NeilBrown
I hope you don't expect too much of a filesystem mounted from such an array
while the other node is writing to the array...

I don't. It will be read-only until the pacemaker RA promotes the slave.
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NeilBrown

2014-10-07 23:33:16 UTC

Hi again. No thoughts here?

Not even 18 hours since you last asked - what do you thing this is? The
Internet :-)

HAHA. I tend to feel ignored on large mailing lists lol. Need to see my therapist again ;)

Post by NeilBrown

Did you try adding the "--readonly" option to your --assemble command?
(Always best to report everything you tried and how it failed - requires less
guess work).

I did that previously and mdadm told me that "option --readonly not valid in assemble mode". E.g. "mdadm --assemble --scan --readonly".

That tells me use are using a version of mdadm earlier than 3.3.
"--assemble --readonly" support was added for 3.3.

NeilBrown

Post by Errol Neal
The readonly flag seems like it can only be used after a device has been assembled. So for example, after the device has been assembled, I can
run mdadm --misc -o /dev/md0 but that is not always safe for my use case.

Post by NeilBrown
I hope you don't expect too much of a filesystem mounted from such an array
while the other node is writing to the array...

I don't. It will be read-only until the pacemaker RA promotes the slave.
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