Re: Promise VTRAK SAN box
- From: "Darren K. Murray" <itech@xxxxxxx>
- Date: Fri, 21 Dec 2007 05:04:11 GMT
Thank you for the clarification. I understand now that many of the functions I was attributing to the initiator and server are actually being done by the target at the other end of the network.
Until recently I had only worked with direct attached storage and I was having a hard time wrapping my head around the low level details of a SAN. Thanks again for taking the time to write.
Spindle wrote:
On Dec 13, 11:58 pm, "Darren K. Murray" <it...@xxxxxxx> wrote:.Hello all,Not a dumb question at all.
I am new to SAN technology and I have what may be a dumb question but
here goes (first a little background):
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 disksThere isn't such a thing as an iSCSI controller or a FC controller for
connected to the network through an iSCSI controller
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 LUNThe 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)Yes
can "see" the storage as a drive letter. Communication over the network
takes place at the block-level.
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 individualOh my! When the target creates a LUN you have no idea on the
logical drives (no RAID), could I remove one of the hard drives, put it
in a PC and see the files?
server if that LUN fits exactly a volume or not.
Or does the server somehow create a "virtualAgain not the server, but the target creates that LUN (no knowledge of
file system" meaning that the only way to access the data on the disks
is via the server?
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.
- References:
- Promise VTRAK SAN box
- From: Darren K. Murray
- Re: Promise VTRAK SAN box
- From: Spindle
- Promise VTRAK SAN box
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