NAS Replication - Time required for 'sync' completion

Asset ID:	1-71-1002803.1
Update Date:	2009-04-22
Keywords:

Solution Type Technical Instruction Sure

Solution 1002803.1 : NAS Replication - Time required for 'sync' completion

Related Items


Sun Storage 5210 NAS Appliance
 Sun Storage 5310 NAS Appliance
 Sun Storage 5320 NAS Gateway/Cluster System
 Sun Storage 5320 NAS Appliance
 Sun Storage 5310 NAS Gateway System

Related Categories


GCS>Sun Microsystems>Storage - Disk>Network Attached Storage

PreviouslyPublishedAs
203827

Description
Under normal circumstances, when using the NAS replication functionality, the most network-intensive processing occurs during the initial block replication - this consists of a block-by-block copy of the source volume disk blocks to the target system (allocated) LUN.

Sufficient time must be allowed (and file volume write activity possibly restricted) for this process to complete.

Steps to Follow
As a first step in creating the mirror, the mirror service attempts to allocate space on the volume for the transaction journal - this may also be referred to as the 'mirror buffer' or, more usually, the 'extended journal'.

The extended journal is a circular buffer - head and tail pointers are used to track points at which the next transaction will be recorded, and which was the last transaction to be successfully synchronized on the mirror volume between the master (source) and mirror (target) NAS systems.

Replication takes place in two distinct phases: Block Replication and Transaction Replication.

Block Replication: The initial replication, after creation of a mirror volume, is a low-level block-by-block copy of the source volume disk blocks to the target system (allocated) LUN. This is achieved 'outside' of the file system, but while it is happening, the master file system records all transactions in the extended journal. The master system cannot begin to send these buffered transactions to the mirror system until the block replication is complete.

Transaction Replication: Once block replication has completed, the mirror begins the steady state of transaction replication. It is during this phase that the master sends complete file system transactions from the extended journal to the mirror system. The mirror system stores each received transaction in its extended journal and acknowledges the reception of the transaction. The mirror system will then asynchronously replay the stored transaction to store the data into its permanent (home) location.

If the (initial) block replication does not complete before the buffer (extended journal) is filled, the only recourse is to restart the block replication.

Recommendations:

1) Ensure private network (subnet or VLAN) is used for 'Replication' link.

2) Ensure extended journal is of sufficient size to hold all transactions(Sun
recommend 10% of the size of the master volume - value used may be smaller)

3) Ensure source and target LUN configuration/performance is optimal.

4) (For WANs) Consider adjustment of TCP window size for better throughput.

Product
Sun StorageTek 5320 NAS Appliance
Sun StorageTek 5210 NAS Appliance
Sun StorageTek 5310 NAS Appliance
Sun StorageTek 5310 NAS Gateway System
Sun StorageTek 5310 NAS Gateway/Cluster System
Sun StorageTek 5320 NAS Gateway/Cluster System

Internal Comments
This document contains normalized content and is managed by the the Domain Lead(s) of the respective domains. To notify content owners of a knowledge gap contained in this document, and/or prior to updating this document, please contact the domain engineers that are managing this document via the “Document Feedback” alias(es) listed below:

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The Knowledge Work Queue for this article is KNO-STO-NAS.

audited, NAS, Replication, Mirror, 5210, 5310. 5320
Previously Published As
88885

Change History
Date: 2007-10-01
User Name: 7058
Action: Approved
Comment: OK to publish.
Spell ck OK.
No tmarks needed.

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