Optimizing SAN

you will get this guidance and requirements from the vendors when you buy the licences/hardware to enable SAN replication


With a suitable fibre link between data centers you can do synchronous replication at block level where it requires a write confirm on both sides before the data is written.
With slower links then asynchronous can be used which will just write to the local copy and send the changes to the other SAN without waiting for confirmation

Is you use this is MS SQL the disks are only presented to one site at a time so writing to the passive site is handled by the SAN

"With a suitable fibre link between data centers you can do synchronous replication at block level where it requires a write confirm on both sides before the data is written."

what i mean is, it is the same problem on all database replication, same set of data update nearly at the same time on both DC, so the database will detect conflict in data and ask DBA which row to keep, this is the main concern.

the idea you can talking about is replication, but what if I have the same set of data update on both side?

"Is you use this is MS SQL the disks are only presented to one site at a time so writing to the passive site is handled by the SAN"

can be active/active ?

A SAN can be simple, or it can be very complex, but its just a storage system, it isnt going to solve this issue "so the database will detect conflict in data and ask DBA which row to keep, this is the main concern."

However if you need simple disk consolidation through to high availability storage with minimal downtime or split site clusters then a SAN can do that, the only limitation are physics and the depth of your pockets.

The experts on Experts-exchange can give you pointers to a total solution (maybe a full solution for a simple requirement) but for a complex multi-site configuration, you will probably benefit from writing a requirement document and sending it to all the local vendors (HP, EMC, NetApps, IBM etc etc) and get them suggest solutions

"A SAN can be simple, or it can be very complex, but its just a storage system
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, it isnt going to solve this "
so can't solve bi  directional replication and conflict ?

"you will probably benefit from writing a requirement document and sending it to all the local vendors (HP, EMC, NetApps, IBM etc etc) and get them suggest solutions
"

this is another good point but experience sharing should be here.

I am wondering how oracle do it as they don't have any thing designed for Multi-site ,shared nothing configuration.

"Well my point is a SAN just provides block or file level storage, yes it can have replication but that's about the blocks and files not about the contents of a DB. That's not to say DB replication at the transaction level cannot be done over a SAN, but it's not an intrinsic function of a SAN"

tks, yeah! should not be that easy or all share nothing DB architecture can't be sale anymore if SAN can handle this.

'"replication ON A SAN which is a very important difference"

is that mean this need another system to do replication and NOT relies on SAN, right?


"TLOG replication is at the application
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 layer, i am not aware of how you would choose with transactions to keep"

it is not Tlog replication but data replication, and the merge of that when same data on both side insert/update nearly at the same time.

I read some internet informatoin and it seems SAN only do reductant storage, fiber switch and multi-pathing, and nothing else a SAN can do ?

"you can have active\active but not with the same Database available at each site"

2 diff oracle instance you mean ?

Replication On a SAN
this is where the data is copied at the Operating System level from one set of disks to another and they happen to be on a SAN. At a basic level this is no different to doing copy and paste from windows explorer

SAN Replication
this is where the data is replicated at the SAN level and it doesn't know or care what the data is, this is "block level replication"


what else are you expecting a SAN to do?
Depending on the vendor and the licences you purchase It does interact with various application but as two people have already suggested you would need to talk to a supplier/vendor about this.

I can only answer clearly for MS SQL as i don't have much Oracle experience but you can have a SQL Cluster that runs active/active with different instances on each server i.e.

Server 1 - instance 1,2 and 5 active, instance 3 and 4 passive
Server 2 - instance 3 and 4 active and instance 1,2 and 5 passive

as IWW said Replication by a SAN and Replication on a SAN are two different things.

Replication by a SAN - This is where the storage controller replicates data at the block level to another storage system, independently and without any intervention of the compute systems attached to the SAN.

Replication over a SAN - This is when an application like Oracle writes its data to two (or more) data stores simultaneously, treating the datastores as just dumb storage, this obviously consumes compute resources as well as storage resources, and is akin to an application reading from one disk and writing to another.

irweazelwallis,

"but you can have a SQL Cluster that runs active/active with different instances on each server i.e.

you are referring to Oracle, right ?

if it is MS SQL, I don't see active/active for that or you talking about DIFF MS SQL instance, right?

i am referring to MS SQL and yes different SQL instances as i said in my last post.

I can only answer clearly for MS SQL as i don't have much Oracle experience but you can have a SQL Cluster that runs active/active with different instances on each server i.e.

Server 1 - instance 1,2 and 5 active, instance 3 and 4 passive
Server 2 - instance 3 and 4 active and instance 1,2 and 5 passive

tks.

so for SAN, it can only do Block level replication but single direction and we need to discuss with vendor on what else it can do.

for replication on SAN it is relies on other factor ,like application level and see if the database can do ? it doesn't related to SAN storage any more for solving merge replication technology.

right ?

that will do as a starting point, you are best off talking to the vendor or any specific SAN you look at to get its capabilities and requirements

and for replication at the application layer is more important that the storage capabilities

tks.

tks