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How does mirroring work within Storage Foundation

Created: 07 Mar 2014 • Updated: 13 Mar 2014 | 3 comments
Marius Gordon's picture
This issue has been solved. See solution.

How does storage foundation mirroring works (technical deep dive)?

How does it sync, Synchronous or asynchronous?

 

In other words, I have a LUN in Datacentre 1 mirrored with a LUN in  Datacentre 2.

Datacentre 2 is 50KM away from Datacentre 1. (Just an example)

Will this slow down the system performance? 

 

Operating Systems:

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mikebounds's picture

Storage foundation mirroring across sites works by have 2 (or more) SAN attached arrays and SF on the node that does the writes, writes to LUNs in both arrays synchronously (i.e the other node at the other site is NOT involved in the write and the node at the other site does not even need to be there to write to both arrays).  Performance is impacted as the write will not be acknowledged until it has written to both arrays and it is not possible to confuiure Storage foundation mirroring to be asynchronous.

If you want asynchronous writes, then you need to use a replication product on the array or the host.  The Veritas implemenation of this is Veritas Volume Replicator and this is an integral part of SF (you cannot use VVR without SF) and is present automatically and just requires a license to use.  VVR ris host-based replication over IP and sends the writes to the secondary host which writes to the array at the secondary site and VVR can be configured as synchronous or asynchronous.

Mike

UK Symantec Consultant in VCS, GCO, SF, VVR, VxAT on Solaris, AIX, HP-ux, Linux & Windows

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SOLUTION
Marianne's picture

In addtion to Mike's excellent post - have you had a look at SFW Admin Guide?

Extract:

About mirroring
A mirrored volume consists of at least two subdisks of identical size located on
separate disks. Each time a file system or application writes to the volume, Veritas
Storage Foundation for Windows transparently writes the same data to each of
the volume’s subdisks.

 
Add Mirror: The primary purpose of mirroring is to provide fault tolerance;
however, mirrored volumes can also improve I/O performance for most
I/O-intensive applications, which make substantially more read requests than
writes. With mirrored volumes, write requests may take longer than with
non-mirrored volumes, but the effects are typically minor.

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