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Discrete Remote Mirroring: Cost Effective Remote Mirroring with Disk Subsystem Based Incremental Instant Copies

IP.com Disclosure Number: IPCOM000131726D
Original Publication Date: 2005-Nov-17
Included in the Prior Art Database: 2005-Nov-17
Document File: 2 page(s) / 18K

Publishing Venue

IBM

Abstract

Modern disk subsystems provide so called instant copies (e.g. IBM FlashCopy, EMC TimeFinder, Hitachi Data Systems NanoCopy ) to freeze the content of a disk on a second disk. For some embodiments of instant copy, the disk subsystems keep track of the changed blocks which differ between the frozen image copy and the original data. We propose to provide a management interface for disk subsystems which allows an external application to extract this list blocks which have changed between two subsequent incremental instant copies. This article describes how two distinct UNIX servers can utilize this new interface, to provide a cost effective remote mirroring services across heterogeneous operating systems and heterogeneous disk subsystem boundaries.

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Discrete Remote Mirroring Discrete Remote MirroringDiscrete Remote Mirroring Discrete Remote Mirroring :

::: Cost Effective Remote Mirroring with Disk SubsystemCost Effective Remote Mirroring with Disk SubsystemCost Effective Remote Mirroring with Disk Subsystem

Cost Effective Remote Mirroring with Disk Subsystem

Based Incremental Instant Copies Based Incremental Instant CopiesBased Incremental Instant Copies Based Incremental Instant Copies

The 'dd' command of the Unix

3 operating system allows to convert a physical disk

into a file. Thus two Unix

                3 servers can provide a remote mirroring service between two disk subsystems which are located in two remote data centers (Fig 1). In a

prototype, we used the netcat command to transfer the file to the remote Unix

3

server. Due to the standardization of the SCSI protocol, this architecture can copy SCSI disks of any operating system and of any disk subsystem to the remote location. We used SAN attached disks which are stored on an IBM 2105 Enterprise

Storage Server

1 and we successfully copied disks for AIX 5.2

1, Linux

4 Mandrake 9.2,

Microsoft Windows 2000

5, Microsoft Windows Server 2003

5, Microsoft Windows XP

5

, and Novel

6 Netware.

          3 server can remotely copy SAN attached SCSI disks using the dd command and the netcat command . The SCSI disk may contain data of any operating system and it can be located on any type of operating system .

    The basic architecture can be enhanced to provide a variant of asynchronous remote mirroring: Modern disk subsystems provide so called instant copies (e.g. IBM

FlashCopy

Fig 1. Two Unix

1, EMC TimeFinder, Hitachi

                        2 Data Systems NanoCopy) to freeze the content of a disk on a second disk. By combining the basic architecture with disk subsystem bases instant copies, the following algorithm continuously updates the SCSI disk at the remote location:

Initialization:

Create instant copy of production data


1.

Use dd and netcat to copy instant copy target volume to remote


2.

    location Mirroring procedure: While true do

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1.


2.


3.

Sleep n minutes

Create new instant copy of production data

Use dd and netcat to copy the refreshed instant copy target volume to

the remote location

    Obviously, this approach consumes a lot of TCP/IP bandwidth between both Unix servers, because for each iteration the complete disk is copied even if only a small amount of data has changed since the previous iteration . A simple enhancement of the management interface of the disk subsystems allows to significantly reduce the amount of consumed TCP...