Re: Promise VTRAK SAN box

On Dec 13, 11:58 pm, "Darren K. Murray" <it...@xxxxxxx> wrote:
Hello all,

I am new to SAN technology and I have what may be a dumb question but
here goes (first a little background):
Not a dumb question at all.

My understanding is that one of the main differences between NAS and SAN
is the location of the file system.

Not quite. A NAS gives you access to a file system using networking
protocols. A SAN gives you access to a virtual volume, a LUN, using
a connectivity protocol suc as iSCSI or FC

NAS appliances have an embedded OS
with 2 or more hard disks formatted with a file system such as NTFS.
Network access to the disks is done using a file-level protocol.

Correct!

SAN appliances such as our Promise VTRAK have a bank of hard disks
connected to the network through an iSCSI controller
There isn't such a thing as an iSCSI controller or a FC controller for
that matter. It helps to think of both protocols as shuttle services
that move data and SCSI commands between two points: an initiator
(the server) and a target (the storage device)

A server on the
network runs an iSCSI initiator to connect to the SAN appliance.

correct so far

mounts the drives,
No, what drives are you talking about? The drives are on the target.
The server cannot mount drives.

creates a LUN
The server doesn't create the LUN, the target does, using extents from
the drives available locally. The server simply gains access to that
LUN via iSCSI

through which Windows (or whatever OS)
can "see" the storage as a drive letter. Communication over the network
takes place at the block-level.
Yes

My question is: with a SAN, where does the file system actually reside?

here is the same conceptual error again: A SAN doesn't know what a
file system is. Your server creates the FS
after making a volume out of a LUN prepared by the iSCSI target and
accessed from (made available thanks to) the iSCSI initiator

In other words, if I had the VTRAK configured as JBOD ie. 15 individual
logical drives (no RAID), could I remove one of the hard drives, put it
in a PC and see the files?
Oh my! When the target creates a LUN you have no idea on the
server if that LUN fits exactly a volume or not.

Or does the server somehow create a "virtual
file system" meaning that the only way to access the data on the disks
is via the server?
Again not the server, but the target creates that LUN (no knowledge of
file systems in a SAN, remember?) so only the target has the pointers
to retrieve that LUN and the coordinates of the file system the
server created

Thank you in advance for any clarification that could be offered.
You're welcome. But feel free to ring again if it's not clear.


.

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