System and method of an efficient snapshot for shared large storage

• US 20060206677A1
• Filed: 05/18/2006
• Published: 09/14/2006
• Est. Priority Date: 07/03/2003
• Status: Abandoned Application

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Kim, Chang Soo, Kim, Young Ho, Kim, Myung Joon, Kang, Dong Jae, Shin, Bum Joo, Bak, Yu Hyeon
• Application Number:
  US11/435,921
• Publication Number:
  US 20060206677A1
• Time in Patent Office: Days
• US Class Current: 711/162
• CPC Class Codes: G06F 11/1466 to make the backup process non-disruptive
• CPC Class Codes: G06F 3/0611 in relation to response time
• CPC Class Codes: G06F 3/0617 in relation to availability
• CPC Class Codes: G06F 3/065 Replication mechanisms
• CPC Class Codes: G06F 3/067 Distributed or networked storage systems, e.g. storage area networks [SAN], network attached storage [NAS]

Abstract

The present invention relates to an efficient snapshot technique based on a mapping for a large logical volume shared in multiple hosts. According to the present invention, problems of time delays in a conventional snapshot technique is solved by employing a FAB and an SSB, which are bits representing whether a COW operation is carried out to a mapping entry. In other words, the present invention solves the problems of delaying a write operation of corresponding volume, which is simultaneously executed when a snapshot is created, until the snapshot creation is completed. Further, in the write operation carried out after the snapshot creation, an operation of determining whether the COW operation is carried out is achieved by reading only an original mapping block by using the FAB and the SSB, without reading out the snapshot mapping block. Therefore, an additional disk access operation is decreased when carrying out a write operation to the volume in which the snapshot exists, thereby improving the performance of operation. Furthermore, in a snapshot destruction operation, the operation of determining whether the COW operation is carried out or not can be achieved without access to the snapshot mapping block, thereby preventing the degradation of performance. In case there is at least one snapshot, the determination operation can be achieved by an access to the original mapping block. Consequently, constant performance is always provided without the number of the snapshots.

Claims

1-3. -3. (canceled)

4. A method of creating a snapshot for on-line backup in a network storage based on a storage area network (SAN), the method comprising the steps of:

changing an volume operation mode of all nodes, in which a mapping server exists, into a snapshot create mode;

locking a mapping block by increasing a value of the mapping block by one;

if the mapping block is not locked, increasing a value of a copy-completed block by one;

unlocking the mapping block; and

if the copy of all the mapping blocks is completed, generating a volume configuration information for the snapshot at an original volume.

5. A method of destroying a snapshot for on-line backup in a network storage based on a storage area network (SAN), the method comprising the steps of:

changing an volume operation mode of all nodes, in which a mapping server exists, into a snapshot destroy mode;

locking a mapping block by increasing a value of the mapping block by one;

determine whether or not a copy-on-write (COW) operation is carried out to a data block, which is indicated by a mapping entry, by using a first allocation bit (FAB) and a snapshot status bit (SSB);

if the COW operation is carried out, initializing the FAB and the SSB, and reflecting a changing of the mapping block in a disk;

unlocking the mapping block; and

if an initialization to all the mapping blocks is completed, destroying a snapshot volume.

6. A method of performing a write operation to a data block of a volume in a network storage based on a storage area network (SAN), the method comprising the steps of:

determining whether a snapshot exists or not and performing a mapping operation;

searching a position of a mapping block, in which a mapping entry of a logical data block being an object of a current write operation exists, and a position of the mapping entry;

reading out the mapping block from a disk and obtaining a value of the desired mapping entry;

checking a value of a first allocation bit (FAB) of the mapping entry to determine whether a data block is first allocated and used after creating the snapshot;

if the value of the FAB is zero and a value of the mapping entry is an initial value, allocating a new block, recording data contents in a copy disk, changing the value of the FAB into one, and reflecting an original mapping block in a disk;

if the data block is allocated before the snapshot, determining whether the COW operation is carried out by using a value of a snapshot status bit (SSB); and

if the COW operation whose value of the SSB is zero is not carried out, performing the COW operation, changing the value of the SSB of the current snapshot into one, and recording the original mapping block in the disk.