[stgt] [PATCH 1/2] tgt-admin: check if direct-device exists before allocating it

[ronnie sahlberg]

On Fri, Sep 12, 2008 at 6:33 PM, FUJITA Tomonori
<fujita.tomonori at lab.ntt.co.jp> wrote:
> On Fri, 12 Sep 2008 18:18:34 +1000
> "ronnie sahlberg" <ronniesahlberg at gmail.com> wrote:
>> the snapshots should have different serial numbers than the
>> original production lun.
>
> I think that it depends what users want. We need to use the same id
> and numbers in some cases (initiators just want to keep using the same
> volume so they don't want to see any changes of scsi id and serial
> number).
>

Yes, but there is also the case where you want to export the snapshot
LUN to the same host as where the production LUN is exported and then
oyu must make sure that they have different identifiers.


I.e.   You have Production LUN 1  exported to host A.
You take a snapshot of LUN 1, and export this point in time snapshot
as LUN 128 to host A.
5 hours later you take another snapshot of LUN 1 and you export this
as LUN 129 to host A.

Host A now sees this device as three different devices : 1   128 129
LUN1 is the real device
LUN 128/129 are read-only point-in-time snapshot copies of the LUN.


Its best to make the snapshots have different serial numbers or
multipath driver might not tell that 128/129 are not the same device.
and there are tears.
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