Reading virtual ordered writes at local storage device

• US 7,380,082 B2
• Filed: 06/26/2003
• Issued: 05/27/2008
• Est. Priority Date: 03/25/2003
• Status: Active Grant

• Current Assignee: Emc IP Holding Company LLC (Dell Technologies Inc.)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Meiri, David, Kopylovitz, Haim, Moreshet, Hana, Yoder, Benjamin W., Halstead, Mark J.
• Primary Examiner(s): Shah; Sanjiv
• Assistant Examiner(s): Campos; Yaima
• Application Number:
  US10/606,699
• Publication Number:
  US 20040193802A1
• Time in Patent Office: 1,797 Days
• Field of Search: 711/113, 711/118, 711/135, 711/141, 711/154, 711161-162, 711/165, 707/10, 707203-204
• US Class Current: 711/162
• CPC Class Codes: G06F 12/0868 Data transfer between cache memory and other subsystems, e.g. storage devices or host systems
• CPC Class Codes: G06F 12/0871 Allocation or management of cache space
• CPC Class Codes: G06F 2212/284 being distributed

Abstract

Using a local storage device to read desired data stored on a remote storage device that receives chunks of data from the local storage device includes, if the desired data is entirely in a cache of the local storage device, the local storage device returning the data from the cache and, if the desired data is not entirely in a cache of the local storage device, reading data from the remote storage device to the local storage device and the local storage device merging the data from the remote storage device with data from the local storage device at the local storage device. Using a local storage device to read desired data stored on a remote storage device that receives chunks of data from the local storage device may also include, prior to reading data from the remote storage device to the local storage device, creating a temporary storage area at the local storage device if there is data from the local storage device that is to be read. The temporary storage area may be a scratch slot.

Claims

1. A method of using a local storage device to read desired data while the data is being transferred from the local storage device to a remote storage device, the method comprising:

if the desired data is entirely in a cache of the local storage device, the local storage device returning the data from the cache, wherein the cache of the local storage device contains data written to the local storage device begun after a first time and before a second time that is associated with a first chunk of data and contains data written to the local storage device begun after the second time that is associated with a second chunk of data different from the first chunk of data and wherein after completion of all writes associated with the first chunk of data, the local storage device initiates transfer of writes associated with the first chunk of data to the remote storage device, an order of the transfer from the local storage device to the remote storage device of data from the first chunk being independent of an order in which data writes of the first chunk are provided to the local storage device; and

if the desired data is not entirely in the cache of the local storage device, reading data from the remote storage device to the local storage device and the local storage device merging the data from the remote storage device with data from the cache of the local storage device at the local storage;

prior to reading data from the remote storage device to the local storage device, creating a temporary storage area at the local storage device if there is data from the local storage device that is to be used;

prior to creating a temporary storage area, locking slots of the local storage device that correspond to data from the local storage device that is to be used;

after merging the data, unlocking the slots of the local storage device that correspond to data from the local storage device that is to be used.

2. A method, according to claim 1, wherein the temporary storage area is a scratch slot.

3. A method, according to claim 1, wherein the data from the local storage area is merged on top of data from the remote storage area.

4. A method, according to claim 1, further comprising:

the remote storage device allocating a temporary storage area in response to data to be read being stored in a cache slot of the remote storage device.

5. A method, according to claim 4, further comprising:

reading data from the disk of the remote storage area into the temporary storage area; and

merging the data to be read stored in the cache slot with data from a disk in the temporary storage area.

6. A method, according to claim 4, further comprising:

prior to the remote storage area determining if there is data to be read stored in a cache slot of the remote storage device, the remote storage device writing at least a portion of the data from at least one cache slot of the remote storage device to a disk of the remote storage device.

7. Computer software, stored in a computer-readable medium, that reads desired data while the data is being transferred from the local storage device to a remote storage device, comprising:

executable code that returns the data from the cache if the desired data is entirely in a cache of the local storage device, wherein the cache of the local storage device contains data written to the local storage device begun after a first time and before a second time that is associated with a first chunk of data and contains data written to the local storage device begun after the second time that is associated with a second chunk of data different from the first chunk of data and wherein after completion of all writes associated with the first chunk of data, the local storage device initiates transfer of writes associated with the first chunk of data to the remote storage device, an order of the transfer from the local storage device to the remote storage device of data from the first chunk being independent of an order in which data writes of the first chunk are provided to the local storage device; and

executable code that reads data from the remote storage device to the local storage device and merges the data from the remote storage device with data from the cache of the local storage device at the local storage device if the desired data is not entirely in the cache of the local storage device;

executable code that creates a temporary storage area at the local storage device if there is data from the local storage device that is to be used prior to reading data from the remote storage device to the local storage device;

executable code that locks slots of the local storage device that correspond to data from the local storage device that is to be used prior to creating a temporary storage area;

executable code that unlocks the slots of the local storage device that correspond to data from the local storage device that is to be used after merging the data.

8. Computer software, according to claim 7, wherein the temporary storage area is a scratch slot.

9. Computer software, according to claim 7, wherein the data from the local storage area is merged on top of data from the remote storage area.

10. Computer software, according to claim 7, further comprising:

executable code that allocates a temporary storage area at the remote storage device in response to data to be read being stored in a cache slot of the remote storage device.

11. Computer software, according to claim 10, further comprising:

executable code that reads data from the disk of the remote storage area into the temporary storage area; and

executable code that merges the data to be read stored in the cache slot with data from a disk in the temporary storage area.

12. Computer software, according to claim 10, further comprising:

executable code that writes at least a portion of the data from at least one cache slot of the remote storage device to a disk of the remote storage device prior to the remote storage area determining if there is data to be read stored in a cache slot of the remote storage device.