Patent Application
20090204759
The present invention relates to computer storage systems, and in particular to consolidating smaller logical unit devices into a large storage volume with minimal impact on the operating system and application software.
In computer storage, a logical unit (LUN) is an address for an individual disk drive and by extension, the disk device itself. The term is used in small computer systems interface (SCSI) protocol to differentiate individual disk drives within a common SCSI target device or disk array. LUN is a common term used in storage area networks (SAN) and other enterprise storage fields. LUN's are not usually used to describe individual disk drives, LUN more often refers to a virtual partition or volume of a RAID set.
Conventional enterprise storage subsystems are capable of storing many terabytes of data. Many users define a standard storage subsystem volume size and create many volumes of this size. Typically, the initial size is small, 8 GB, for example. As more storage is allocated the number of these small LUN's grows very quickly. For example, an IBM DS8000 with a capacity of 512 T byte could contain 48,000, 8 G byte units. A very large number of storage subsystem volumes results in management complexity. Larger storage subsystem volumes may reduce management complexity to some extent. There is currently no way to resolve this problem, without an off-line conversion of the smaller volumes into larger ones, backup and restore of data from the server, and potential reconfiguration of all software and applications on the server. IBM's SAN Volume Controller (SVC) provides the ability to migrate storage extents (a multiple of blocks) between the “physical” storage subsystem disks it presents to the host operating system.
In SCSI, LUN's are addressed in conjunction with the controller ID of the host bus adapter, the target ID of the storage array, and an optional slice ID. In UNIX operating systems, such ID's are often combined, e.g., to refer to a controller, a target, a disk, and a slice, all in one word. EMC, Sun's Solaris operating system, Hewlett Packard's HP-UX, Hitachi Data Systems, NCR, and Teradata's MP-RAS use LUN slices, while IBM's AIX uses “hdiskN” to refer to a particular partition of a storage device.
Conventional storage volume consolidation processes require application downtime, and backup and restore of data. The prior art methods do not work while the system is on-line. Such prior art methods also require significant changes to the existing software or applications.
A storage subsystem device driver for an operating system includes a trap mechanism for intercepting calls from a host with a computer operating system into logical unit devices that were previously consolidated into a single physical volume. A map converts such calls to a logical unit device into a corresponding offset in the consolidated single physical volume. A driver accesses the single physical volume with corresponding offsets to transfer data associated with a particular logical unit device. Logical unit devices can be consolidated and reconsolidated to single physical volumes and other physical volumes without requiring changes to the operating system or its application software.
The invention allows storage volumes, which are normally a combination of physical disks, to be consolidated into a single logical entity and easily managed by storage administrators.
A method is provided that allows storage administrators to freely select the storage volumes to be consolidated and to carry out the consolidation process.
Also provided is a method that can be executed without any downtime or system outage by maintaining a table which maps the original storage subsystem volumes to offsets in new single, consolidated volumes, thereby allowing I/O operations to the previous volumes to be transparently redirected to new consolidated volumes.
Also provided is a method by which a storage subsystem can notify affected hosts of storage configuration changes, thus allowing logical volume managers to change their internal storage mapping to access newly-created consolidated storage volumes.
The above summary of the present invention is not intended to represent each disclosed embodiment, or every aspect, of the present invention. Other aspects and example embodiments are provided in the figures and the detailed description that follow.
The present invention may be more completely understood in consideration of the following detailed description of various embodiments of the present invention in connection with the accompanying drawings, in which:
In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part hereof, and within which are shown by way of illustration specific embodiments by which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention.
In
In
One embodiment of a method consolidates smaller logical volumes into a large physical volume of an appropriate size. For each volume to be consolidated, an offset into the new volume, e.g., LUN 210, is determined for current volumes 201-206. The blocks of storage are copied one at a time from each current volume hdisk1-hdisk6 devices 201-206, into the corresponding partitions hdisk1-hdisk6 partitions 211-216, on consolidated volume 210. Such steps are repeated until all the blocks of all the original volumes have been coalesced into the new volume 210. If a device discovery process were run after this operation, only the single LUN 210 would be discovered. Applications that formerly accessed volumes using hdisk1-hdisk6 devices 201-206 would now fail.
In one embodiment a device driver is used to map previous device names to the offset within the newly created LUN. In
Input/Output (I/O) requests from a host to a consolidated volume are mapped by a device driver to an offset into the newly created volume. In a step 402, the application issues an I/O read or write request, e.g., to any of hdisk1-hdisk6. The device driver intercepts the I/O, in a step 404. The device driver, in a step 406, converts the operating system device ID to an appropriate physical location, e.g., as in Table-I.
The device driver, e.g., 304, executes access to the appropriate location, in a step 408. In a step 410, the device driver receives an indication of success, such as an acknowledgment (ACK), from the storage subsystem. The device driver returns success, e.g., ACK, to the application in a step 412.
Table-II illustrates how the map in Table-I could be adjusted to accommodate a change in the consolidation volumes, e.g., two physical volumes (LUN A and B) instead of one. The operating system would be unaffected by such change, because it can continue to use OS device ID's “hdisk1” thru “hdisk6”.
In an alternative to a device driver approach, the storage subsystem could perform the consolidation and redirect host requests for the original LUN ID to the offset into the consolidated LUN. After consolidation, a method 500 in
In addition to device drivers on the host and code running in the storage subsystem, the invention can be implemented as a part of any firmware in a storage adapter installed in a host, or as part of an operating system that includes logical volume managers and file systems.
While the present invention has been described with reference to several particular example embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention, which is set forth in the following claims.
