question about ceph and FC SAN LUN data IO path

question about ceph and FC SAN LUN data IO path

[Dennis Chen]

Hi,

If I have an OSD attached by a FC SAN device with the connection like this:
OSD HBA-->FC Switch-->SAN storage device.

Then Map a LUN in the SAN to the OSD as its only disk device to save 
data. if I have a client also has an HBA and the topology diagram looks 
like:

                   osd                                         client
         -------        -------                            -------     
-------
        | HBA |      | NIC |  <---------------> | NIC |   | HBA |
         ---+---      --------                            ------- -------
\                                                            /
                   \ /
                        \                                   /
                               \    --------------
                                   | FC Switch |
                                    --------------
                                           |
                                        SAN

Suppose the created LUN above for OSD can be accessed by both osd and 
client though FC I/F, the question is:
if I create a rbd block device in osd and map it to client, make a file 
system and mount it in client side, then create a file in the mounted 
FS. The read/write operation followed for this file will transfer data 
though ethernet path or FC path?

BRs,
Dennis

Re: question about ceph and FC SAN LUN data IO path

[Wido den Hollander]

On 05/13/2013 02:24 PM, Dennis Chen wrote:
> Hi,
>
> If I have an OSD attached by a FC SAN device with the connection like this:
> OSD HBA-->FC Switch-->SAN storage device.
>
> Then Map a LUN in the SAN to the OSD as its only disk device to save
> data. if I have a client also has an HBA and the topology diagram looks
> like:
>
>                    osd                                         client
>          -------        -------                            ------- -------
>         | HBA |      | NIC |  <---------------> | NIC |   | HBA |
>          ---+---      --------                            ------- -------
> \                                                            /
>                    \ /
>                         \                                   /
>                                \    --------------
>                                    | FC Switch |
>                                     --------------
>                                            |
>                                         SAN
>
> Suppose the created LUN above for OSD can be accessed by both osd and
> client though FC I/F, the question is:
> if I create a rbd block device in osd and map it to client, make a file
> system and mount it in client side, then create a file in the mounted
> FS. The read/write operation followed for this file will transfer data
> though ethernet path or FC path?
>

That will follow the Ethernet path.

I'm also trying to figure out why you would Ceph here and use RBD? If 
the client has direct access to the FC, why not have the client access 
that direcly?

Ceph makes sense when you are running it on multiple fully separated 
machines, but not if you run it all one one FC SAN imho.

Wido

> BRs,
> Dennis
>
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-- 
Wido den Hollander
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