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Storage Consolidation:Storage consolidation, also called storage convergence is a method of centralizing data storage among multiple servers. The objective is to facilitate data backup and archiving for all subscribers in an enterprise, while minimizing the time required to access and store data. Other desirable features include simplification of the storage infrastructure, centralized and efficient management, optimized resource utilization, and low operating cost.
Consolidated Storage Scenarios
There are a number of ways in which Storage technologies can help your organization consolidate storage, and help you to save time and money.
•NAS Gateway to a SAN: Consolidating File and Block Storage. For large organizations that have a SAN, curtailing the proliferation of NAS devices for file storage can be accomplished by deploying a NAS gateway (head) to the SAN. NAS gateways connect to the IP network and communicate with storage arrays on the SAN through switching technology. NAS gateways do not have on board storage; rather they access storage on the SAN, translating file data from the server into blocks for storage (and the reverse, when the data is requested by the server) as necessary. Deployment of a NAS gateway can help administrators to centralize block and file storage, while at the same time lowering equipment acquisition costs and preserving the value of NAS storage investments.
•Consolidated Backup Infrastructure. Consolidating storage onto a network provides administrators the opportunity to consolidate both backup hardware and software, helping organizations realize considerable cost savings.
On the hardware end, a SAN can support a single automated tape library with multiple tape drives, eliminating the need for backup equipment on each server, and centralizing media administration processes. Because the backup process has been moved off the servers and off the LAN, backups no longer impact work schedules or bandwidth.
By using Windows the Volume Shadow Copy Service, snapshot technologies can be integrated with the backup process, helping to ensure high fidelity backups and significantly reduce the backup window. Backups are stored centrally on the SAN; if a server goes down a second server can access the shadow copy and make it available for use. Not only does this simplify backup management, but it also speeds time to restore dramatically.
•Consolidate SAN Islands. Although SANs can scale to large sizes, it is more common for organizations to deploy multiple SANs, dedicating each SAN to a specific mission-critical database application, or each SAN serving a separate department or remote site location. Without interconnection, each of these SANs must be protected and managed independently, increasing cost and complexity. Islands of Fibre Channel SAN can be connected by extending the Fibre Channel infrastructure between them; however across long distances, this is an expensive proposition. (This is not a problem for iSCSI SANs, because no special equipment is required.) A less expensive solution is to use the existing LAN to extend a connection between distant SANs and an iSCSI bridge to translate between iSCSI and Fibre Channel protocols.
For full details on how to do this using the Microsoft iSCSI software, see the section "iSCSI Bridge to a Fibre Channel SAN" in the white paper Deploying iSCSI SANs with the Microsoft iSCSI Architecture.
•Low Cost Consolidation of Wintel Servers to Centralized Storage. The centralized storage benefits—localized rather than distributed backups, reduced administration and simplified management—of a Fibre Channel SAN can be inexpensively extended to legacy servers. Rather than installing costly Fibre Channel HBAs to connect to the SAN, the standard IP networking equipment (onboard network interface cards) and the Microsoft iSCSI initiator coupled with an iSCSI gateway facilitates connection to the SAN.
•Blade Servers. In deployments that require hundreds or thousands of servers, managing individual servers is an administrative nightmare—server hardware acquisition and maintenance costs are high, and software update distribution is its own full time job. Blade (thin) servers are designed to share hardware resources among servers in a rack; the thinnest blade servers are diskless servers which access consolidated storage resources from the storage network.
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DEFINITIONS OF TERMS USED ALL THROUGHOUT THIS BLOG
A node is a computer attached to a SAN.
A SAN is a high-speed subnetwork of shared storage devices.
Software that manages San file system functions, such as file locking, space allocation, and data access authorization, is called the Metadata controller.(This is an Apple Storage implementation term - other companies use other terms)
Metadata controller uses callbacks to communicate with file system clients.
Xsan file system client software runs on all nodes in the SAN and communicates with the metadata controller in order to provide Xsan services. The term file system client refers to a node that is running the Xsan file system client software.
A redundant array of independent disks (RAID) device is a category of disk devices that combines two or more drives increased for fault tolerance and performance. There are several RAID levels:
*Level 0 provides data striping, where blocks of a file are spread across multiple disks, increasing performance; this level does not have any provisions that increase fault tolerance.
*Level 1 provides disk mirroring.
*Level 3 provides the data striping of Level 0 and also reserves a disk for storing error correction data, thereby increasing performance and fault tolerance.
*Level 5 provides data striping at the byte level and maintains stripe error correction information.
A JBOD (just a bunch of disks) is a disk that is not configured for RAID.
A logical unit number (LUN) is an aggregation of physical devices. Applications access LUNs through the special files in the system’s /dev/disk directory. For RAID devices, a LUN is typically a RAID-5 with three or more physical drives making up the LUN. For JBOD devices, one JBOD is one LUN.
A storage pool is a grouping of LUNs that have the same characteristics. Another term for storage pool is stripe group. One or more storage pools form a mountable volume. The number of volumes hosted by a single Xsan metadata controller should not exceed eight.
Stripe depth is the number of disks that have been assigned to a storage pool.
The stripe breadth is the maximum amount of data that is read or written before switching to the next LUN in the storage pool. When the last LUN is reached, I/O operations go back to t he first LUN. This is how large logical I/O operations are broken down into stripes across multiple LUNs. For example, if the stripe breadth for a storage pool is set at 4 MB, each I/O operation on that storage pool is physically no more than 4 MB. A 16 MB I/O operation would be broken down into 4 physical I/O operations.
A stripe line is the stripe breadth multiplied by the number of LUNs in the storage pool. To maximize performance, make I/O requests that area stripe line in size.
For real-time I/O, well-formed I/O is I/O that is a stripe line in size. This size makes the best utilization of the disks in the storage pool and maximizes the transfer rate. For non-real-time I/O, well-formed I/O is I/O that is memory aligned (modulus 4 bytes), 512-byte sector aligned, and modulus sector sized.
A block is the smallest number of bytes that can be read or written.
Storage pools can be assigned one or more values, known as an affinity identifiers, and a file can be assigned one affinity. When a request is made to allocate space in a file for which the affinity has been set, the space is allocated from the storage pool that an affinity identifier that matches the file’s affinity. For example, consider a SAN with some moderate performance JBOD LUNs and some high performance RAID-5 LUNs. By grouping the RAID-5 LUNs into the same storage pool and assigning them a specific affinity identifier, the developer can steer performance critical data to that storage pool. Files containing less critical data or files that do not have an affinity are assigned to the storage pool that consists of JBOD LUNs.
When a storage pool is in real-time I/O mode, file system clients that have processes that do non-real-time I/O must request a non-real-time I/O token Xsan throttles the speed of I/O of applications that are not in real-time mode so that their I/O does not interfere with real-time I/O. This document uses the term gate to describe processes or file descriptors that are not in real-time I/O mode and the term ungated to describe processes or file descriptors that are in real-time I/O mode.
An extent is a chunk of file data whose allocation is contiguous on a storage pool. A file’s data may be stored in one or more extents. Information about an extent includes its file-relative starting byte offset, its file system starting byte offset, the file system ending byte offset, and the ordinal of the storage pool on which the extent resides. File system clients use extent mapping tables to load information about a file’s extents. Loading extent information improves performance by eliminating a subsequent trip by the file system client to the metadata controller in order to retrieve extent information for the range mapped by an I/O request.
When there are two or more storage pools that have the same characteristics, an allocation strategy is needed. The strategy can be to round-robin files through the set of storage pools, balance the remaining space in the storage pools, or fill the first storage pool before going to the next storage pool.
A disk file system, such as a UFS or HFS+ file system, resides on the internal drives of a computer or on storage devices that are attached directly to the computer. A network file system allows data on internal drives or on directly attached drives to be shared with other computers on the network. Examples of network file systems include Apple Filing Protocol (AFP), Server Message Block (SMB), Common Internet File System (CIFS), or Network File System (NFS). A distributed file system is a blend of disk file system and network file system used to simplify data sharing through the creation of a single shared name space across a collection of servers. A cluster file system gives multiple computers simultaneous, very high-speed access to all shared data residing on an external, centralized storage pool. The storage pool typically consists of highly available RAID systems. Xsan is a cluster file system
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