Block storage device having hierarchical disks with different access frequencies
A first block storage device sharing an object storage device with a second block storage device has: plural kinds of physical devices having different access response performances; and a hierarchical logical disk created by using the storage areas of the physical devices and the storage area of the object storage device. When the access frequency of a logical block stored in a hierarchy one level above a lowest hierarchy falls below a threshold, the first block storage device searches the object storage device for a logical block having the hash of the logical block as a content address. When the search fails, the first block storage device transmits the logical block to the object storage device to change a hierarchy to store the logical block to the lowest hierarchy, whereas when the search succeeds, omits the transmission and changes a hierarchy to store the logical block to the lowest hierarchy.
1. A storage system comprising:
a first block storage device accessed by a first host computer, and a second block storage device accessed by a second host computer, the first block storage device and the second block storage device sharing an object storage device having a content addressable storage (CAS) function of providing a cloud service,
wherein
the first block storage device includes:
a first hierarchical logical disk composed of a plurality of first logical blocks and created by using storage areas of plural kinds of first physical devices and a storage area of the object storage device, with the object storage device as a lowest hierarchy and the plural kinds of first physical devices having different access response performances as a plurality of hierarchies above the lowest hierarchy;
a first deduplication unit configured to, when access frequency of a first logical block stored in a hierarchy one level above the lowest hierarchy is reduced to fall below a threshold, do a search of the object storage device for a logical block having a hash of the first logical block as a content address; and
a first hierarchy changing unit configured to, when the search by the first deduplication unit fails, perform transmission of the first logical block to the object storage device for storing the first logical block in the object storage device and thereby change a hierarchy to store the first logical block to the lowest hierarchy, whereas when the search by the first deduplication unit succeeds, omit the transmission and change a hierarchy to store the first logical block to the lowest hierarchy, and
the second block storage device includes:
a second hierarchical logical disk composed of a plurality of second logical blocks and created by using storage areas of plural kinds of second physical devices and a storage area of the object storage device, with the object storage device as a lowest hierarchy and the plural kinds of second physical devices having different access response performances as a plurality of hierarchies above the lowest hierarchy;
a second deduplication unit configured to, when access frequency of a second logical block stored in a hierarchy one level above the lowest hierarchy is reduced to fall below the threshold, do a search of the object storage device for a logical block having a hash of the second logical block as a content address; and
a second hierarchy changing unit configured to, when the search by the second deduplication unit fails, perform transmission of the second logical block to the object storage device for storing the second logical block in the object storage device and thereby change a hierarchy to store the second logical block to the lowest hierarchy, whereas when the search by the second deduplication unit succeeds, omit the transmission and change a hierarchy to store the second logical block to the lowest hierarchy.
2. The storage system according to claim 1 , wherein:
the second block storage device has:
a first backup area corresponding to the lowest hierarchy of the first hierarchical logical disk; and
a first backup control unit configured to, upon receiving a search request designating a content address from the first block storage device, do a search of the first backup area for a logical block having the content address, return a search result to the first block storage device, and store a logical block received from the first block storage device into the first backup area with use of the hash of the logical block as a content address;
the first deduplication unit is configured to transmit a search request to the second block storage device and thereby do a search of the first backup area for a logical block having the content address; and
the first hierarchy changing unit is configured to, when the search of the first backup area by the first deduplication unit fails, transmit the logical block to the second block storage device in order to store the logical block into the first backup area.
3. The storage system according to claim 2 , wherein:
the first block storage device has:
a second backup area corresponding to the lowest hierarchy of the second hierarchical logical disk; and
a second backup control unit configured to, upon receiving a search request designating a content address from the second block storage device, do a search of the second backup area for a logical block having the content address, return a search result to the second block storage device, and store a logical block received from the second block storage device into the second backup area with use of the hash of the logical block as a content address;
the second deduplication unit is configured to transmit a search request to the first block storage device and thereby do a search of the second backup area for the logical block having the content address; and
the second hierarchy changing unit is configured to, when the search of the second backup area by the second deduplication unit fails, transmit the logical block to the first block storage device in order to store the logical block into the second backup area.
4. The storage system according to claim 2 , wherein
the first backup control unit is configured to, when the search of the first backup area for the logical block fails, search for a second logical block which is stored in the hierarchy one level above the lowest hierarchy of the second hierarchical logical disk and in which the hash of the second logical block matches the content address of the logical block that the search fails, and decrease access frequency of the second logical block found through the search.
5. A data management method in a storage system, the storage system including a first block storage device accessed by a first host computer, and a second block storage device accessed by a second host computer, the first block storage device and the second block storage device sharing an object storage device having a content addressable storage (CAS) function of providing a cloud service, the first block storage device including a first hierarchical logical disk composed of a plurality of first logical blocks and created by using storage areas of plural kinds of first physical devices and a storage area of the object storage device, with the object storage device as a lowest hierarchy and the plural kinds of first physical devices having different access response performances as a plurality of hierarchies above the lowest hierarchy, the second block storage device including a second hierarchical logical disk composed of a plurality of second logical blocks and created by using storage areas of plural kinds of the second physical devices having different access response performances and a storage area of the object storage device, with the object storage device as a lowest hierarchy and the plural kinds of second physical devices as a plurality of hierarchies above the lowest hierarchy,
the method comprising:
by the first block storage device,
when access frequency of a first logical block stored in a hierarchy one level above the lowest hierarchy is reduced to fall below a threshold, doing a search of the object storage device for a logical block having a hash of the first logical block as a content address;
when the search fails, performing transmission of the first logical block to the object storage device to store the first logical block in the object storage device and thereby changing a hierarchy to store the first logical block to the lowest hierarchy; and
when the search succeeds, omitting the transmission of the first logical block to the object storage device and change a hierarchy to store the first logical block to the lowest hierarchy.
6. The method according to claim 5 , wherein the second block storage device has a first backup area corresponding to the lowest hierarchy of the first hierarchical logical disk, and
the method further comprises:
by the first block storage device,
transmitting a search request to the second block storage device and thereby doing a search of the first backup area for a first logical block having the content address; and
when the search of the first backup area fails, transmitting the first logical block to the second block storage device in order to store the first logical block into the first backup area.
7. The method according to claim 6 , wherein the first block storage device has a second backup area corresponding to the lowest hierarchy of the second hierarchical logical disk, and
the method further comprises:
by the second block storage device,
transmitting a search request to the first block storage device and thereby doing a search of the second backup area for a second logical block having the content address; and
when the search of the second backup area fails, transmitting the second logical block to the first block storage device in order to store the second logical block into the second backup area.
8. The method according to claim 6 , further comprising:
by the second block storage device,
when the search of the first backup area for the logical block fails, doing a search for a second logical block which is stored in the hierarchy one level above the lowest hierarchy of the second hierarchical logical disk and in which the hash of the second logical block matches the content address of the logical block that the search fails, and decreasing access frequency of the second logical block found through the search.