Question about the use of PERSISTENT RESERVATION IN/OUT

Question about the use of PERSISTENT RESERVATION IN/OUT

[Brian Auld]

I was able to acquire some level of understanding of the use of "persistent
reservation in/out" commands after having read some SCSI specs and browsing
this mailing list's archives. I have made some presumptions and wanted 
to run
them by this list to make sure I wasn't too far out in left field.
                                                                               
I'm designing a linux-based application that is going to use LUNs for 
storage
from a backend FC SAN. It's not very sexy, but there is a one to one
relationship for i) boxes running my appl and ii) LUNs. One of the 
requirements
that has been imposed on the appl is that once a given backend LUN has been
assigned to my application, any other physical entity (i.e. a different
initiator on a different box, which could be running my appl) is to be
prevented from accessing this LUN using some kind of protection mechanism.
                                                                               
Once a LUN is assigned to a specific box running my appl, this protection
should exist until I explicitly deassign this LUN in my user interface. In
other words, the protection should persist across host reboots and target
reset/reboots.
                                                                               
I have made the following assumptions and decisions about how this will be
handled:
                                                                               
1) As I understand it, there is no reserve/release (persistent or old)
mechanism in the scsi subsystem itself.
                                                                               
2) WRT (1), there are however 2 mechanisms for sending pass-through commands
through the scsi subsystem directly to a target device: namely, (i) using an
sg device or (ii) sd ioctls.
                                                                               
3) What I would like to do is setup my application so the following 
occurs when
a LUN is assigned/deassigned to my appl:
                                                                               
assigned:
-------------
In my appl, send an appropriate combination of PERSISTENT RESERVE 
OUT(service
action: reserve ...) commands to effectivly lock this device so that any
initiator not included in the list I provide will be prevented from 
accessing
my LUN. I would use the sg mechanism or sd ioctls to do this.
                                                                               
deassigned:
---------------
In my appl, send an appropriate combination of PERSISTENT RESERVE OUT 
(service
action: release) commands to free up this LUN. Again, I would use sd ioctls
or the sg mechanism to do this.
                                                                               
Is this basic approach flawed? It would seem to be doable based on what 
I have
read so far, but I don't know for sure.
                                                                               
Any feedback would be appreciated.
                                                                               
Thanks,
Brian

Question about the use of PERSISTENT RESERVATION IN/OUT

[Brian Auld]

Sorry for the initial staggered email.

I was able to acquire some level of understanding of the use of "persistent
reservation in/out" commands after having read some SCSI specs and browsing
this mailing list's archives. I have made some presumptions and wanted 
to run
them by this list to make sure I wasn't too far out in left field.


I'm designing a linux-based application that is going to use LUNs for 
storage
from a backend FC SAN. It's not very sexy, but there is a one to one
relationship for i) boxes running my appl and ii) LUNs. One of the 
requirements
that has been imposed on the appl is that once a given backend LUN has been
assigned to my application, any other physical entity (i.e. a different
initiator on a different box, which could be running my appl) is to be
prevented from accessing this LUN using some kind of protection mechanism.


Once a LUN is assigned to a specific box running my appl, this protection
should exist until I explicitly deassign this LUN in my user interface. In
other words, the protection should persist across host reboots and target
reset/reboots.


I have made the following assumptions and decisions about how this will be
handled:


1) As I understand it, there is no reserve/release (persistent or old)
mechanism in the scsi subsystem itself.


2) WRT (1), there are however 2 mechanisms for sending pass-through commands
through the scsi subsystem directly to a target device: namely, (i) using an
sg device or (ii) sd ioctls.


3) What I would like to do is setup my application so the following 
occurs when
a LUN is assigned/deassigned to my appl:


assigned:
-------------
In my appl, send an appropriate combination of PERSISTENT RESERVE 
OUT(service
action: reserve ...) commands to effectivly lock this device so that any
initiator not included in the list I provide will be prevented from 
accessing
my LUN. I would use the sg mechanism or sd ioctls to do this.


deassigned:
---------------
In my appl, send an appropriate combination of PERSISTENT RESERVE OUT 
(service
action: release) commands to free up this LUN. Again, I would use sd ioctls
or the sg mechanism to do this.


Is this basic approach flawed? It would seem to be doable based on what 
I have
read so far, but I don't know for sure.


Any feedback would be appreciated.


Thanks,
Brian

Re: Question about the use of PERSISTENT RESERVATION IN/OUT

[Brian Auld]

Thanks for your feedback and suggestions.

I take it from the first reply that the basic mechanism of implementing
persistent reservation out/in (regardless of the nitty gritty) using sg or
sd ioctls is doable? I guess my really big question is can I do this at 
all?
For now, I primarily want to make sure that the facilities (i.e. sg) are
there to implement something.

Is support/non-support for sg (or sd ioctls) adapter driver specific? or is
it supported for any device that plugs into the scsi stack?

Brian


Qi, Yanling wrote:

> 1. You need to issue PROUT (service action: register) first before 
> issuing PROUT reserve service action.
> 2. If you would like only one initiator port to access the LUN, the 
> reservation type should be "Exclusive Access".
> 3. You need to decide whether or not you need to "break" a 
> reservation. PROUT release service action can only release the 
> reservation that owns by this valid registrant but can not clear 
> somebody else's reservation.
>
> Yanling
>
> -----Original Message-----
> From: Brian Auld [mailto:bauld@lefthandnetworks.com]
> Sent: Thursday, April 01, 2004 3:07 PM
> To: linux-scsi@vger.kernel.org
> Subject: Question about the use of PERSISTENT RESERVATION IN/OUT
>
>
> Sorry for the initial staggered email.
>
> I was able to acquire some level of understanding of the use of 
> "persistent
> reservation in/out" commands after having read some SCSI specs and 
> browsing
> this mailing list's archives. I have made some presumptions and wanted
> to run
> them by this list to make sure I wasn't too far out in left field.
>
>
> I'm designing a linux-based application that is going to use LUNs for
> storage
> from a backend FC SAN. It's not very sexy, but there is a one to one
> relationship for i) boxes running my appl and ii) LUNs. One of the
> requirements
> that has been imposed on the appl is that once a given backend LUN has 
> been
> assigned to my application, any other physical entity (i.e. a different
> initiator on a different box, which could be running my appl) is to be
> prevented from accessing this LUN using some kind of protection 
> mechanism.
>
>
> Once a LUN is assigned to a specific box running my appl, this protection
> should exist until I explicitly deassign this LUN in my user 
> interface. In
> other words, the protection should persist across host reboots and target
> reset/reboots.
>
>
> I have made the following assumptions and decisions about how this 
> will be
> handled:
>
>
> 1) As I understand it, there is no reserve/release (persistent or old)
> mechanism in the scsi subsystem itself.
>
>
> 2) WRT (1), there are however 2 mechanisms for sending pass-through 
> commands
> through the scsi subsystem directly to a target device: namely, (i) 
> using an
> sg device or (ii) sd ioctls.
>
>
> 3) What I would like to do is setup my application so the following
> occurs when
> a LUN is assigned/deassigned to my appl:
>
>
> assigned:
> -------------
> In my appl, send an appropriate combination of PERSISTENT RESERVE
> OUT(service
> action: reserve ...) commands to effectivly lock this device so that any
> initiator not included in the list I provide will be prevented from
> accessing
> my LUN. I would use the sg mechanism or sd ioctls to do this.
>
>
> deassigned:
> ---------------
> In my appl, send an appropriate combination of PERSISTENT RESERVE OUT
> (service
> action: release) commands to free up this LUN. Again, I would use sd 
> ioctls
> or the sg mechanism to do this.
>
>
> Is this basic approach flawed? It would seem to be doable based on what
> I have
> read so far, but I don't know for sure.
>
>
> Any feedback would be appreciated.
>
>
> Thanks,
> Brian
>
>
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