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EMC SANCopy, Clone, Snapshot question



 
 
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  #1  
Old January 2nd 06, 05:02 AM posted to comp.arch.storage
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Default EMC SANCopy, Clone, Snapshot question

I am new to this SAN stuff as we just got a CX500 and CX300 installed by
Dell. I am trying to get my arms around the SANCopy, Clone and Snapshot
concepts. I know that they are different but I don't know how. Can someone
explain them to me?

The way I understand it is if I did a "Clone" of a source LUN from the CX500
to the CX300 at a DR site I would have an exact copy of the source LUN.
(i.e. If the source LUN had 500GB of data so would the "clone" LUN).
So what happens if I did a SANCopy of that same LUN to that same remote LUN?
Wouldn't it still be 500GB?

So what's the differance? And what will Snapshots do for me?

We also have a mount host at the DR site. We have two Exchange 2003
clusters on the SAN and two Windows 2000 file server hosts connected to the
SAN right now.

Thanks for any input,


Clayton


  #2  
Old January 3rd 06, 04:04 AM posted to comp.arch.storage
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Default EMC SANCopy, Clone, Snapshot question

Clayton,
Clone is within the same array. You can't "clone" to a different array.
You
use MirrorView for that purpose. SANCopy is (typically a one-time
operation)
used to copy bulk data from a Clariion to another storage array (target

doesn't have to be a Clariion).
Snapshots are point in time copy of the source lun. Once you take a
snapshot and activate it, any changes made to the original source
lun are tracked in a special lun called cache or reserve lun. The cache
lun is typically 10-15% of the source lun and holds the blocks that
have been
changed in the original lun.

HTH

  #3  
Old January 4th 06, 01:54 AM posted to comp.arch.storage
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Default EMC SANCopy, Clone, Snapshot question

Thanks for your reply Madhu,

Okay, I think I understand the Clone (and MirrorView) concept. You would
use it when you wanted another copy of you data on-site. But if you want to
push a copy off-site (maybe to a DR site) then your would have to use
SANCopy. Do I have that right? But what do you mean the SANCopy is
"typically" a one time operation? If you are using SANCopy don't/can't you
use it to schedule a SANCopy nightly if you want?

SnapShots - Okay, I can relate to most of that. But, if the original sourse
LUN changes and the changes are tracked in the cache LUN when is it written
to the source or Snapshot?


Thnaks for all of your help,


Clayton


wrote in message
ups.com...
Clayton,
Clone is within the same array. You can't "clone" to a different array.
You
use MirrorView for that purpose. SANCopy is (typically a one-time
operation)
used to copy bulk data from a Clariion to another storage array (target

doesn't have to be a Clariion).
Snapshots are point in time copy of the source lun. Once you take a
snapshot and activate it, any changes made to the original source
lun are tracked in a special lun called cache or reserve lun. The cache
lun is typically 10-15% of the source lun and holds the blocks that
have been
changed in the original lun.

HTH



  #4  
Old January 5th 06, 07:33 AM posted to comp.arch.storage
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Default EMC SANCopy, Clone, Snapshot question

Hey HVB,

Thanks for your input.

Rather than beat about the bush with the possible merits of various
functions, can you tell us what you're trying to do with your storage?


Here is what we are trying to do. In our data center we have a CX500 and a
Disk Array Enclosure fully populated with disk. We have two Exchange 2003
clusters and two file servers on this SAN for now. We have EMC Replication
Manager/SE , SANCopy and SnapView. At our DR site we have another SAN that
has an CX300 with a Disk Array Enclosure fully populated with disk (same
amount of disk space that's on the data center SAN).

The idea when we bought all of this was to "push" in some fashion, our
production data to the DR site. Dell came in and set all of this up but
didn't do a knowledge transfer so we are kinda left to figure out how all of
this works. We are trying to understand and figure the best way to get the
data to the DR site (EMC Replication Manager/SE , SANCopy, SnapView or
MirrorView) However, we didn't buy "MirrorView" so that's not really an
options for us I guess.

Dell set up "Replication" jobs for all of the data transfer and ran the jobs
as a test once. After that they said we could setup what ever schedule we
wanted. We also have a "Mount Host" at the DR site. It is part of the AD
domain and just has Windows 2003 and EMC Replication Manager/SE on it. It
is also connected into the SAN.

So I just need some "ideas" on how to do what we want to do. I am trying to
understand the difference between SANCopy, SnapView and MirrorView and when
I should use which.


Thanks a bunch for all of your help,


Clayton



"HVB" wrote in message
...
On Wed, 04 Jan 2006 00:54:56 GMT, "Clayton Sutton" wrote:

Okay, I think I understand the Clone (and MirrorView) concept. You would
use it when you wanted another copy of you data on-site.


That's what MirrorView does, yes. A clone is like MirrorView, in that
it's a complete copy of the source LUN, but the data is copied to a
new LUN within the same array.

But if you want to
push a copy off-site (maybe to a DR site) then your would have to use
SANCopy. Do I have that right?


Maybe...

But what do you mean the SANCopy is
"typically" a one time operation? If you are using SANCopy don't/can't
you
use it to schedule a SANCopy nightly if you want?


Typically you'd use SANCopy to push data off an (old) array onto a
(new) EMC Clariion. The idea generally being that you'd stop using
the old array.

Note that with SAN Copy you can move data from selected non-EMC arrays
to a Clariion and vice-versa.

You'd only use this regularly if you wanted to push data to/from a
non-EMC array. This could be scheduled if you wanted. To relate back
to your example, you *could* use SAN Copy to push data to a non-EMC
array at a remote location (like a DR centre).

If you have two similar EMC arrays (i.e. two Clariions) we'd expect to
use MirrorView to push the data between the arrays.

The exception to this is if you're using EMC Replication Manager/SE to
create application-level (Exchange or SQL) replication groups - in
that case you *might* use SAN Copy. == note this is fairly unusual
and there are other (EMC) ways of doing Exchange/SQL replication.

SnapShots - Okay, I can relate to most of that. But, if the original
sourse
LUN changes and the changes are tracked in the cache LUN when is it
written
to the source or Snapshot?


With SnapShots changes are always written to the source LUN. The old
data from the source is written into the 'cache' LUN, really known as
the 'reserved LUN pool'


HVB



  #5  
Old January 12th 06, 08:59 PM posted to comp.arch.storage
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Default EMC SANCopy, Clone, Snapshot question

HVB ) wrote:
: SnapShot = *virtual* point-in-time copy of your source volume/LUN. The
: size overhead for a snapshot depends on the rate of change of data in
: your source volume/LUN. A high change rate will consume more disk
: space than a low change rate.

When snapshots are made is any effort made to ensure that the snapshot is
started at a point where the file system on that LU is in a consistent state?
If not, it seems like the snapshots carry a risk associated with them that
when a problem is detected the file system may not guaranteed to be in a
consisten state on some (and worst case all) of the snapshots. If it does
ensure the file system is in a consistent state then how does it detect this?

Dave

  #6  
Old January 12th 06, 09:28 PM posted to comp.arch.storage
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Default EMC SANCopy, Clone, Snapshot question

Microsoft's VSS (Volume Shadow Service) solves this by notifying the VSS
aware apps (MSSQLServer, Exchange, some Windows-embedded database engines) that
the snapshot is about to be created. For instance, SQL server can do the
checkpoint and stall all disk writes before snapping, and continue normal work
after snapping.

Without the VSS-aware snapshot engine (and VSS-aware apps), the write
inactivity timeout is the only way.

--
Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation

http://www.storagecraft.com

"Dave Sheehy" wrote in message
...
HVB ) wrote:
: SnapShot = *virtual* point-in-time copy of your source volume/LUN. The
: size overhead for a snapshot depends on the rate of change of data in
: your source volume/LUN. A high change rate will consume more disk
: space than a low change rate.

When snapshots are made is any effort made to ensure that the snapshot is
started at a point where the file system on that LU is in a consistent state?
If not, it seems like the snapshots carry a risk associated with them that
when a problem is detected the file system may not guaranteed to be in a
consisten state on some (and worst case all) of the snapshots. If it does
ensure the file system is in a consistent state then how does it detect this?

Dave


 




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