Data Storage - Basic SAN Question...

Author

Basic SAN Question...

dave_roland_mann@yahoo.com

2005-06-14, 8:47 pm

I am trying to settle an argument at the office and I am hoping that
one of you can answer the question for me. It is fairly basic as I am
new to this whole SAN thing.

Suppose that I have two windows servers, each connected to a sepearte
LUN on an MSA1000 (each server can see his LUN but not the other
servers). Both servers and the disk are connected to a SAN switch.

Suppose I want to copy data from the SAN LUN on servera to the SAN LUN
on server b.

Does it work this this
servera -> SAN -> serverb

or
servera -> SAN -> LAN -> serverb

What data goes over the LAN and what goes over the SAN?

Thanks
Dave

Ramesh Pun

2005-06-14, 8:47 pm

it work this this
servera -> SAN -> serverb

<dave_roland_mann@yahoo.com> wrote in message
news:1118793314.637893.15960@f14g2000cwb.googlegroups.com...
>I am trying to settle an argument at the office and I am hoping that
> one of you can answer the question for me. It is fairly basic as I am
> new to this whole SAN thing.
>
> Suppose that I have two windows servers, each connected to a sepearte
> LUN on an MSA1000 (each server can see his LUN but not the other
> servers). Both servers and the disk are connected to a SAN switch.
>
> Suppose I want to copy data from the SAN LUN on servera to the SAN LUN
> on server b.
>
> Does it work this this
> servera -> SAN -> serverb
>
> or
> servera -> SAN -> LAN -> serverb
>
> What data goes over the LAN and what goes over the SAN?
>
> Thanks
> Dave
>

dave_roland_mann@yahoo.com

2005-06-15, 2:46 am

Thanks for the quick response. Does it matter how I copy the data.
For example, mapping a drive or ftp? Say I make a request to copy a
large file from servera to serverb. Servera says I need the data off
the LUN, sends it through the HBA to the FC switch which says hey I
know where that LUN is and sends it to the appropriate LUN. Even
though servera cannot see the LUN for serverb the switch knows where
the LUN is at. Is this correct?

Sorry if this is a dumb question. I just want to make sure that I have
it.

Thanks Again
Dave

Bill Todd

2005-06-15, 2:46 am

dave_roland_mann@yahoo.com wrote:
> Thanks for the quick response. Does it matter how I copy the data.
> For example, mapping a drive or ftp? Say I make a request to copy a
> large file from servera to serverb. Servera says I need the data off
> the LUN, sends it through the HBA to the FC switch which says hey I
> know where that LUN is and sends it to the appropriate LUN. Even
> though servera cannot see the LUN for serverb the switch knows where
> the LUN is at. Is this correct?

Not unless you're running some very unusual software in both servers and
in the switch and/or the MSA1000: otherwise, the only entities that
know exactly *where* to get the data and *where* to put it are the
servers (and, incidentally, they're also the only ones *allowed* to do
things like that, because there's usually no mechanism to coordinate
concurrent accesses to their file systems with another entity such as
the switch), and since each can see only its own LUN Server a has to
obtain the data, send it (presumably over the LAN) to Server b, which
then writes it to its own LUN.

>
> Sorry if this is a dumb question.

Don't worry: it's already elicited one blatantly incorrect answer,
which places at least some kind of bound on how 'dumb' it can be.

- bill

Charles Morrall

2005-06-15, 2:46 am

<dave_roland_mann@yahoo.com> skrev i meddelandet
news:1118793314.637893.15960@f14g2000cwb.googlegroups.com...
>I am trying to settle an argument at the office and I am hoping that
> one of you can answer the question for me. It is fairly basic as I am
> new to this whole SAN thing.
>
> Suppose that I have two windows servers, each connected to a sepearte
> LUN on an MSA1000 (each server can see his LUN but not the other
> servers). Both servers and the disk are connected to a SAN switch.
>
> Suppose I want to copy data from the SAN LUN on servera to the SAN LUN
> on server b.
>
> Does it work this this
> servera -> SAN -> serverb

No.
>
> or
> servera -> SAN -> LAN -> serverb
>
Yes.

> What data goes over the LAN and what goes over the SAN?
>
All data goes across the LAN. Nothing goes over the SAN as I think you mean
it, but of course the data gets transferred to/from each server across the
LAN and then to/from the MSA1000 over the SAN.

All the SAN is that you have (meaning you probably don't have any
third-party software or filesystem or some such) is a SCSI bus on a network.
Heck, Fibre Channel is a SCSI-3 protocol.

> Thanks
> Dave
>

themeanies

2005-06-15, 5:50 pm

dave_roland_mann@yahoo.com wrote:
> I am trying to settle an argument at the office and I am hoping that
> one of you can answer the question for me. It is fairly basic as I am
> new to this whole SAN thing.
>
> Suppose that I have two windows servers, each connected to a sepearte
> LUN on an MSA1000 (each server can see his LUN but not the other
> servers). Both servers and the disk are connected to a SAN switch.
>
> Suppose I want to copy data from the SAN LUN on servera to the SAN LUN
> on server b.
>
> Does it work this this
> servera -> SAN -> serverb
>
> or
> servera -> SAN -> LAN -> serverb
>
> What data goes over the LAN and what goes over the SAN?
>
> Thanks
> Dave
>

Think of the SAN as a very complex IDE or SCSI cable.
Now think of the LUN's in your SAN as an IDE or SCSI disk drive on that
cable.

For your scenario above it's the same as transferring data from an
internal disk on one PC to an internal disk on a second lan attached PC.
There is no way for the first PC to see the hard disks in the second PC
without going through the LAN and OS.

Note this is not the case in Clustering where 2 or more hosts are
attached to the same LUN for failover. But I don't think this is where
you were headed.
There does also exists Snap copies and mirroring and other such
functions to copy LUNs across the SAN but afaik these are not used on a
file level, but on a LUN level.

So let's see if I can draw your scenario.

ServerA attached to LUN-A, OS calls it the D: drive
ServerB attached to LUN-B, OS calls it the G: drive

ServerA maps a drive across the LAN to ServerB's G: drive calling it E:

On ServerA you xcopy a file from D: to E: and this is the path it takes:

LUN-A -> SAN -> ServerA -> LAN -> ServerB -> SAN -> LUN-B

FWIW, here's what happens with a LUN mirror/copy which is a function of
your SAN's storage processor.

ServerA attached to LUN-A, OS calls it the D: drive
ServerB attached to LUN-B, OS calls it the G: drive

A LUN mirror/copy is initiated to mirror LUN-A to LUN-B. This data
transfer is done over part of the SAN(inside the SAN's storage
processor). When it's completed, and provided there has been no IO to
the source and destination LUNs, ServerA's LUN-A and ServerB's LUN-B
will be identical. Effectively you've copied data across the SAN.

So data flows like this:

LUN-A -> Storage Processor -> LUN-B

Snap images are similar, but the snap image is an array of pointers to
the source data for reading vs. full IO. Takes up less space than a
full mirror of a LUN.

ServerA attached to LUN-A, OS calls it the D: drive
ServerB attached to LUN-B, OS calls it the G: drive

LUN-B is a snap image of LUN-A instead of a separate LUN.

On ServerB you copy a file from G: to a local C: drive and the data
flows like this:

LUN-A -> Storage Processor -> SAN -> ServerB -> Local disk C: on ServerB

Effectively you've copied data from ServerA's LUN-A to ServerB without
going over the LAN.

hth,
tM

Kat

2005-06-15, 5:50 pm

I think you have it wrong- it doesn't use the switch per se, it uses the
LAN- it would be the sanme as copying it from one server to another that was
NOT SAN attached.

Personally, I jus copy from server to server, I don't use FTP. But that's
just me. You aren't getting any more eprformance copying from san disk to
san disk than if you were copying local to local.

--
Kat
MCDBA # ? of Millions

What woud you do for a Kit Kat bar?
<dave_roland_mann@yahoo.com> wrote in message
news:1118802026.448555.273660@z14g2000cwz.googlegroups.com...
> Thanks for the quick response. Does it matter how I copy the data.
> For example, mapping a drive or ftp? Say I make a request to copy a
> large file from servera to serverb. Servera says I need the data off
> the LUN, sends it through the HBA to the FC switch which says hey I
> know where that LUN is and sends it to the appropriate LUN. Even
> though servera cannot see the LUN for serverb the switch knows where
> the LUN is at. Is this correct?
>
> Sorry if this is a dumb question. I just want to make sure that I have
> it.
>
> Thanks Again
> Dave
>

Maxim S. Shatskih

2005-06-15, 5:50 pm

FTP is much faster then SMB/CIFS while copying major amounts of data from
the server to the server.

--
Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
maxim@storagecraft.com
http://www.storagecraft.com

"Kat" <kit-kat bar> wrote in message news:42b08b5e$1@obsidian.gov.bc.ca...
> I think you have it wrong- it doesn't use the switch per se, it uses the
> LAN- it would be the sanme as copying it from one server to another that was
> NOT SAN attached.
>
> Personally, I jus copy from server to server, I don't use FTP. But that's
> just me. You aren't getting any more eprformance copying from san disk to
> san disk than if you were copying local to local.
>
> --
> Kat
> MCDBA # ? of Millions
>
> What woud you do for a Kit Kat bar?
> <dave_roland_mann@yahoo.com> wrote in message
> news:1118802026.448555.273660@z14g2000cwz.googlegroups.com...
>
>

Nik Simpson

2005-06-15, 5:50 pm

<dave_roland_mann@yahoo.com> wrote in message
news:1118793314.637893.15960@f14g2000cwb.googlegroups.com...

> Does it work this this
> servera -> SAN -> serverb
>
> or
> servera -> SAN -> LAN -> serverb
>
> What data goes over the LAN and what goes over the SAN?

With two servers each mounting their respective LUNs as local filesystems
there is no way for the basic OS to perform anything other than:

Lun1(SAN)->Server A ->CIFS/NFS-> Server B -> Lun2(SAN)

Direct SAN to SAN copy would require a block level copy and would be done in
the array.

--
Nik Simpson

Nik Simpson

2005-06-15, 5:50 pm

"Ramesh Pun" <spamme@spamme.com> wrote in message
news:11av1k25a2no21@corp.supernews.com...
> it work this this
> servera -> SAN -> serverb

And just what mechanism in the OS would that happen, inquiring minds want to
know.

--
Nik Simpson

Ramesh Pun

2005-06-17, 2:48 am

I guess we need to define what a SAN is then.

For me a SAN is all the fabric components (HBA, switch, storage).

The only thing I would correct in that little diagram is make the arrows
double headed.

serverA <-> SAN <-> serverB

Now, we can expand the SAN

HBA-serverA <-> Switch <-> Storage <-> Switch <-> HBA-serverB

Now, the fact that server A and server B cant see each others storage is
secondary.
The config is correct.

If you wanted to copy data from serverA's LUN to serverB's LUN, you dont
necessarily have to go over a LAN link, you could do it with the storage
box. HP has business copy, EMC has time finder, I am sure IBM has some other
technology as well.

"Nik Simpson" <n_simpson@bellsouth.net> wrote in message
news:Ah2se.90515$lQ3.88937@bignews5.bellsouth.net...
>
> "Ramesh Pun" <spamme@spamme.com> wrote in message
> news:11av1k25a2no21@corp.supernews.com...
>
> And just what mechanism in the OS would that happen, inquiring minds want
> to know.
>
>
> --
> Nik Simpson
>

Ramesh Pun

2005-06-17, 2:48 am

Oh Man,
I cant believe the level of knowledge about SAN's that exists here.
If I had known I would have defined it in more layman terms

"Bill Todd" <billtodd@metrocast.net> wrote in message
news:wZKdnccM18SABTLfRVn-uw@metrocastcablevision.com...
> dave_roland_mann@yahoo.com wrote:
>
> Not unless you're running some very unusual software in both servers and
> in the switch and/or the MSA1000: otherwise, the only entities that know
> exactly *where* to get the data and *where* to put it are the servers
> (and, incidentally, they're also the only ones *allowed* to do things like
> that, because there's usually no mechanism to coordinate concurrent
> accesses to their file systems with another entity such as the switch),
> and since each can see only its own LUN Server a has to obtain the data,
> send it (presumably over the LAN) to Server b, which then writes it to its
> own LUN.
>
>
> Don't worry: it's already elicited one blatantly incorrect answer, which
> places at least some kind of bound on how 'dumb' it can be.
>
> - bill

Bill Todd

2005-06-17, 2:48 am

Ramesh Pun wrote:
> Oh Man,
> I cant believe the level of knowledge about SAN's that exists here.
> If I had known I would have defined it in more layman terms

It seems that your command of English is no better than your
understanding of storage architecture: 'layman' is not a synonym for
'accurate'.

- bill

Bill Todd

2005-06-17, 2:48 am

Ramesh Pun wrote:
> I guess we need to define what a SAN is then.

No, Nik and others here understand that quite well, thank you.

>
> For me a SAN is all the fabric components (HBA, switch, storage).
>
> The only thing I would correct in that little diagram is make the arrows
> double headed.
>
> serverA <-> SAN <-> serverB
>
> Now, we can expand the SAN
>
> HBA-serverA <-> Switch <-> Storage <-> Switch <-> HBA-serverB
>
> Now, the fact that server A and server B cant see each others storage is
> secondary.
> The config is correct.

Only as far as it goes, which is not far enough to answer the original
question.

>
> If you wanted to copy data from serverA's LUN to serverB's LUN, you dont
> necessarily have to go over a LAN link, you could do it with the storage
> box.

No, you could not.

If you wanted to copy *the entire contents of servera's LUN to serverb's
LUN* (destroying whatever already happened to be present on serverb's
LUN in the process), then yes, with appropriate snapshot (in case
servera might want continued update access to its LUN during the
operation) and copy support in the storage box, and some interface to
that support, and agreement from serverb that it would leave its LUN
alone while all this was going on you could do so.

But when someone talks about 'copying data' (as distinct from, say,
'copying the LUN') they're usually talking about file-level operations,
and indeed Dave's subsequent response made that very clear.

- bill

Ramesh Pun

2005-06-17, 2:48 am

"Bill Todd" <billtodd@metrocast.net> wrote in message
news:pKudnVWL2_u61C_fRVn-3Q@metrocastcablevision.com...

> But when someone talks about 'copying data' (as distinct from, say,
> 'copying the LUN') they're usually talking about file-level operations,
> and indeed Dave's subsequent response made that very clear.
>
> - bill

semantics......

I guess what we have established is that theres more than one way to skin
the SAN 'cat'.

Nik Simpson

2005-06-17, 5:47 pm

"Ramesh Pun" <spamme@spamme.com> wrote in message
>
> semantics......
>
> I guess what we have established is that theres more than one way to skin
> the SAN 'cat'.
But only one of those ways is relevant when answering the original question.
If we are all allowed to redefine the original question to fit whatever
answer we happen give then this is going to become a forum of limited to
value(tm).

--
Nik Simpson

Dave Sheehy

2005-06-22, 5:47 pm

Charles Morrall (charles.morrall@telia.com) wrote:

: Heck, Fibre Channel is a SCSI-3 protocol.

Technically speaking that is not correct. An analogous and equally incorrect
statement would be "Ethernet is a file storage protocol". FCP is a SCSI-3
protocol that uses Fibre Channel as the underlying network interconnect
just as Ethernet is the underlying network interconnect for NFS.

Dave