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From: Chris Ridd on 18 Jan 2010 14:38
On 2010-01-18 19:32:55 +0000, Zfs.. said:

> On Jan 18, 5:20 pm, Darren Dunham <darren.dun...(a)gmail.com> wrote:
>> On Jan 18, 9:00 am, "Zfs.." <cian.scrip...(a)gmail.com> wrote:
>>
>>> While doing some testing we noticed that we where able to import the
>>> same zpool using the -f option to two separate machines at the same
>>> time.
>>
>> Given the "-f" option means "force", that doesn't surprise me.  You
>> can do the same thing with Symantec Volume manager and the correct
>> flags as well.
>
> Thanks for the reply Darren. I do understand that I'm issuing a force
> of the pool, and of course you must be sure that if you use this flag
> you better know what you are doing. However, with zfs, this is the
> ONLY way to import the pool to another host which seems funny to me.
> Correct me if I'm wrong, but this has been my experience with zfs.

You're supposed to run zfs export on the original host. Are you doing that?

--
Chris

From: Zfs.. on 18 Jan 2010 14:43
On Jan 18, 7:38 pm, Chris Ridd <chrisr...(a)mac.com> wrote:
> On 2010-01-18 19:32:55 +0000, Zfs.. said:
>
>
>
>
>
> > On Jan 18, 5:20 pm, Darren Dunham <darren.dun...(a)gmail.com> wrote:
> >> On Jan 18, 9:00 am, "Zfs.." <cian.scrip...(a)gmail.com> wrote:
>
> >>> While doing some testing we noticed that we where able to import the
> >>> same zpool using the -f option to two separate machines at the same
> >>> time.
>
> >> Given the "-f" option means "force", that doesn't surprise me.  You
> >> can do the same thing with Symantec Volume manager and the correct
> >> flags as well.
>
> > Thanks for the reply Darren. I do understand that I'm issuing a force
> > of the pool, and of course you must be sure that if you use this flag
> > you better know what you are doing. However, with zfs, this is the
> > ONLY way to import the pool to another host which seems funny to me.
> > Correct me if I'm wrong, but this has been my experience with zfs.
>
> You're supposed to run zfs export on the original host. Are you doing that?
>
> --
> Chris

In normal operation we do, we where just testing some stuff and
decided to try something that we thought wouldn't work. And it did ??

Thats why I opened the thread. We would normally always export the
pool, however to import it to another system you still have to issue -
f as far as I am aware. I dont have access to any systems at the
moment to confirm this !
From: Richard B. Gilbert on 18 Jan 2010 15:01
Zfs.. wrote:
> On Jan 18, 5:26 pm, "Richard B. Gilbert" <rgilber...(a)comcast.net>
> wrote:
>> Zfs.. wrote:
>>> Folks,
>>> Some worrying behavior with zfs.
>>> While doing some testing we noticed that we where able to import the
>>> same zpool using the -f option to two separate machines at the same
>>> time.
>>> The zpool resides on SAN storage that both servers can see. Importing
>>> the zpool to one machine is no problem, but while imported there we
>>> can also import it to the second machine.. This is not good.
>>> We then decided to be wicked and mounted a filesystem on one side,
>>> wrote a file into it and then on the other side ran a scrub.. Needless
>>> to say, the server that tried to do the scrub crashed.
>>> So, basically, besides the obvious comment of "just don't do that", is
>>> there a way to "lock" a zpool down to a particular machine while it is
>>> imported ?
>>> I think you should be able to do this because if not then there is
>>> potential for some disastrous situations to arrive.
>>> Any thoughts are welcome !
>> Historically, Unix has been deficient in "locking" just about anything.
>> The last time I looked it was possible for two users to open a file with
>> write access at the same time. I cheerfully admit that it has been
>> years since I last looked!
>>
>> Be prepared for disaster BEFORE you experiment!
>
> Hi Richard,
>
> Yes, we have been prepared for disaster, and have encountered it many
> times while testing. It's all fun though. Right ?
>
> :-)

It can be. But when your boss wants to know "What happened to my
files?" the fun is over!
From: nelson on 18 Jan 2010 16:18
back when we first started playing with ZFS we experienced similar
behaviour, even attempting to export the pool will cause a panic.

i have a vague recollection that it was resolved through patching and
we haven't seen that sort of thing for a couple of years now - what
release are you running and do you patch?

while we've corrupted a few pools through dodgy SAN equipment
flapping, i don't think we've actually destroyed data through the
panic but that may have just been luck....we tend not to use the -f
flag or NOINUSE_CHECK anymore except in extreme circumstances
From: Darren Dunham on 18 Jan 2010 17:11
On Jan 18, 11:32 am, "Zfs.." <cian.scrip...(a)gmail.com> wrote:
> Thanks for the reply Darren. I do understand that I'm issuing a force
> of the pool, and of course you must be sure that if you use this flag
> you better know what you are doing. However, with zfs, this is the
> ONLY way to import the pool to another host which seems funny to me.
> Correct me if I'm wrong, but this has been my experience with zfs.

Not if it has been exported.

While the pool is in use (imported), it marks the pool as in use by
the particular host. Any other host trying to import will fail. If
the original host exports the pool that lock is cleared.

There's really not any good way to tell the difference between
"really" in use, and "was in use a while ago, but not in use any
longer". The system simply sets and clears the in-use flag.

> If you issue zpool import mypool on a pool that was accessed on
> another system it will tell you to use the -f option.

If it hasn't been explicitly exported, yes. If you're expecting to
use this on multiple systems, doing a clean export should be part of
your workflow so that you don't have to force the import.

> This is something I think Sun need to look at, surely there has to be
> another way to do this without issuing -f to the import.

Assuming you're exporting it, there should be no problem.

--
Darren
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