Data synchronization among file storages using stub files

• US 8,856,073 B2
• Filed: 12/14/2010
• Issued: 10/07/2014
• Est. Priority Date: 12/14/2010
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Matsuzawa, Keiichi
• Primary Examiner(s): LU, KUEN S
• Application Number:
  US12/967,677
• Publication Number:
  US 20120150799A1
• Time in Patent Office: 1,393 Days
• Field of Search: 707/622
• US Class Current: 707/622
• CPC Class Codes: G06F 16/119 Details of migration of file systems migration mechanisms in storage systems G06F3/0647
• CPC Class Codes: G06F 16/1744 using compression, e.g. sparse files
• CPC Class Codes: G06F 16/178 Techniques for file synchronisation in file systems
• CPC Class Codes: G06F 16/1787 Details of non-transparently synchronising file systems
• CPC Class Codes: G06F 16/185 Hierarchical storage management [HSM] systems, e.g. file migration or policies thereof details of archiving G06F16/11
• CPC Class Codes: G06F 3/0607 by facilitating the process of upgrading existing storage systems, e.g. for improving compatibility between host and storage device
• CPC Class Codes: G06F 3/0647 Migration mechanisms
• CPC Class Codes: G06F 3/067 Distributed or networked storage systems, e.g. storage area networks [SAN], network attached storage [NAS]

Abstract

A method switches file server from old file server to new file server which are coupled via a backend network and provides data synchronization. The old file server and new file server are coupled with one or more host computers via a frontend network to direct input/output (I/O) requests from the one or more host computers. The method comprises creating stub files in the new file server, the stub files including stub information indicating location of data in the old file server; switching I/O requests directed to old file server to I/O requests directed to the new file server; checking whether the new file server has any stub files; and, if the new file server has one or more stub files, recalling data corresponding to the one or more stub files from the old file server according to the stub information to replace the one or more stub files.

Claims

1. A method for switching file servers from an old file server to a new file server, the old file server managing a file system which includes a plurality of directories and files, the method comprising:

creating a stub file of a root directory of the file system in the new file server;

switching a direction of requests, targeting to the plurality of directories and files of the file system, from the old file server to the new file server, after creating the stub file of the root directory in the new file server and before creating all of the other stub files of the plurality of directories and files in the file system;

receiving a request at the new file server;

checking whether the new file server has any stub files for a target of the request; and

if the new file server has one or more stub files for the target of the request,

recalling data corresponding to the one or more stub files for the target of the request from the old file server according to stub information indicating location of data to replace the one or more stub files with the recalled data.

2. The method according to claim 1, further comprising:

continuing requests to the file servers during the switching, checking, and recalling.

3. The method according to claim 1, further comprising, prior to creating the stub file in the new file server:

copying data from the old file server to a storage media and, installing the storage media containing the copied data in the new file server;

storing in the new file server a copy date timestamp corresponding to the copying of data from the old file server to the storage media;

checking a flag, corresponding to each file or directory in the new file server, as NO indicating that the data in the file or directory are not latest in the new file server;

checking whether any file or directory in the new file server has a corresponding flag NO indicating that the data therein are not latest in the new file server; and

for each file or directory with a NO flag, checking the flag as YES in the new file server, and if the copy date timestamp for data in the file or directory is older than a target timestamp of the corresponding file or directory in the old file server indicating that data of the corresponding file or directory in the old file server has been overwritten at the target timestamp which is newer than the copy date timestamp, removing data of the file or directory in the new file server and performing the creating stub files in the new file server for the file or directory.

4. The method according to claim 1, wherein an external file server is coupled with the new file server via a backend network, the method further comprising, after recalling data corresponding to the one or more stub files from the old file server having the data according to the stub information:

migrating files of the recalled data to the external file server.

5. The method according to claim 1, further comprising:

receiving, by the new file server, a request for a file;

determining whether the file of the request is a stub file in the new file server;

if the file is not a stub file and the request is not a write request, processing the request to access data in the new file server;

if the file is a stub file and the request is not a write request, recalling data corresponding to the stub file from the old file server according to the stub information to replace the one or more stub files; and

if the request is a write request, writing data of the write request to the new file server.

6. The method according to claim 5, wherein an external file server is coupled with the new the server via a backend network, the method further comprising:

migrating data of the request to an external file server.

7. The method according to claim 1, further comprising:

receiving, by the new file server, a request for a directory;

creating one or more stub files for one or more files under the requested directory in the new file server by reading metadata from the old file server.

8. A new file server in an information system which further includes an old file server coupled with the new file server, the old file server managing a file system which includes a plurality of directories and files, the new file server comprising:

a memory; and

a processor configured to;

create a stub file of a root directory of the file system in the new file server,;

start to receive a request targeting to the plurality of directories and files of the file system,

after creating the stub file of the root directory in the new file server and before creating all of the other stub files of the plurality of directories and files in the file system; and

upon receiving a request targeting to the plurality of directories and files of the file system by the new file server,

check whether the new file server has any stub files for a target of the request and,

if the new file server has one or more stub files for the target of the request,

recall data corresponding to the one or more stub files for the target of the request from the old file server according to stub information indicating location of data to replace the one or more stub files with the recalled data.

9. The new file server according to claim 8, further comprising:

a storage media containing data copied from the old file server and installed in the new file server;

wherein the memory stores a copy date timestamp corresponding to the copying of data from the old file server to the storage media;

wherein the processor is configured, prior to creating stub files in the new file server, to

check a flag, corresponding to each file or directory in the new file server, as NO indicating that the data in the file or directory are not latest in the new file server;

check whether any file or directory in the new file server has a corresponding flag NO indicating that the data therein are not latest in the new file server; and

for each file or directory with a NO flag, check the flag as YES in the new file server, and if the copy date timestamp for data in the file or directory is older than a target timestamp of the corresponding file or directory in the old file server indicating that data of the corresponding file or directory in the old file server has been overwritten at the target timestamp which is newer than the copy date timestamp, remove data of the file or directory in the new file server and create stub files in the new file server for the file or directory.

10. The new file server according to claim 8,

wherein the processor is configured, after recalling data corresponding to the one or more stub files from the old file server having the data according to the stub information, to migrate files of the recalled data to an external file server.

11. The new file server according to claim 8, wherein the processor is configured, upon receiving a request for a file to:

determine whether the file of the request is a stub file in the new file server;

if the file is not a stub file and the request is not a write request, process the request to access data in the new file server;

if the file is a stub file and the request is not a write request, recall data corresponding to the stub file from the old file server according to the stub information to replace the one or more stub files; and

if the request is a write request, write data of the write request to the new file server.

12. The new file server according to claim 11, wherein the processor is configured to:

migrate data of the request to an external file server.

13. The new file server according to claim 8, wherein the processor is configured, upon receiving a request for a directory, to create one or more stub files for one or more files under the requested directory in the new file server by reading metadata from the old file server.

14. An information system comprising:

an old file server managing a file system which includes a plurality of directories and files;

a new file server; and

a backend network coupling the old file server and the new file server;

wherein the new file server is configured to create a stub file of a root directory of the file system in the new file server;

start to receive a request targeting to the plurality of directories and files of the file system, after creating the stub file of the root directory in the new file server and before creating all of the other stub files of the plurality of directories and files in the file system; and

upon receiving a request targeting to the plurality of directories and files of the file system,

check whether the new file server has any stub files for a target of the request and,

if the new file server has one or more stub files for the target of the request,

recall data corresponding to the one or more stub files for the target of the request from the old file server according to stub information indicating location of data to replace the one or more stub files with the recalled data.