DATA ARCHIVING USING DATA COMPRESSION OF A FLASH COPY

• US 20130205109A1
• Filed: 03/14/2013
• Published: 08/08/2013
• Est. Priority Date: 11/19/2010
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: BENHASE, Michael T., GUPTA, Lokesh M., HSU, Yu-Cheng, SANCHEZ, Alfred E.
• Granted Patent: US 8,914,597 B2
• Time in Patent Office: Days
• US Class Current: 711/162
• CPC Class Codes: G06F 11/1076 Parity data used in redundant arrays of independent storages, e.g. in RAID systems
• CPC Class Codes: G06F 2211/1014 Compression, i.e. RAID systems with parity using compression techniques
• CPC Class Codes: G06F 3/065 Replication mechanisms

Abstract

Embodiments of the disclosure relate to archiving data in a storage system. An exemplary embodiment comprises making a flash copy of data in a source volume, compressing data in the flash copy wherein each track of data is compressed into a set of data pages, and storing the compressed data pages in a target volume. Data extents for the target volume may be allocated from a pool of compressed data extents. After each stride worth of data is compressed and stored in the target volume, data may be destaged to avoid destage penalties. Data from the target volume may be decompressed from a flash copy of the target volume in a reverse process to restore each data track, when the archived data is needed. Data may be compressed and uncompressed using a Lempel-Ziv-Welch process.

Claims

1. A computer implemented method for archiving data, comprising:

making a first flash copy of data in a first storage volume while the first storage volume is off-line;

compressing data in the first flash copy, wherein each track of data is compressed into a set of data pages; and

storing the set of compressed data pages into a second storage volume.

2. The method of claim 1, wherein the first flash copy is made in a background operation.

3. The method of claim 1, wherein making a first flash copy comprises:

marking the second storage volume as write-inhibit;

allocating for the second storage volume a data extent from a pool of compressed data extents; and

allocating a new data extent from the compressed data extent pool when there is no more free space in the allocated data extent to store the compressed data.

4. The method of claim 3, further comprising updating a volume structure to indicate that the compressed data extent is allocated to the second storage volume.

5. The method of claim 3, wherein data in the first flash copy is compressed using Lempel-Ziv-Welch (LZW) compression.

6. The method of claim 1, further comprising reading data to be compressed from the first storage volume if the data to be compressed is not in the first flash copy.

7. The method of claim 1, further comprising destaging the compressed data once a stride worth of data has been compressed and stored in the second storage volume.

8. The method of claim 3, further comprising deallocating any unused extents allocated for the second storage volume.

9. The method of claim 1, further comprising uncompressing archived data in the second storage volume.

10. The method of claim 9, wherein uncompressing comprises:

making a second flash copy of compressed data in the second storage volume, the second flash copy comprising the sets of compressed data pages wherein each set of pages corresponds to a track of uncompressed data in the first storage volume;

uncompressing data in each set of pages in the second flash copy into the corresponding track of uncompressed data; and

storing the uncompressed data track in the first storage volume.

11. The method of claim 10, wherein making a second flash copy comprises:

marking the first volume as write-inhibit;

allocate for the first volume a data extent from a pool of uncompressed data extents; and

allocating a new data extent from the uncompressed data extent pool when there is no more free space in the allocated data extent to store the uncompressed data.

12. The method of claim 10, further comprising deallocating any unused extents allocated to the first storage volume.

13. The method of claim 10, further comprising reading data to be uncompressed from the second storage volume if the data to be uncompressed is not in the second flash copy.

14. The method of claim 9, further comprising destaging the uncompressed data once a stride worth of data has been uncompressed and stored in the first storage volume.

15. The method of claim 9, wherein the archived data is uncompressed using Lempel-Ziv-Welch (LZW) uncompression.