User manual APPLE XSAN ADMINISTRATOR GUIDE

[. . . ] Xsan Administrator's Guide Includes information for managing Xsan volumes in a storage area network using Xsan Admin or the command line Apple Computer, Inc. The owner or authorized user of a valid copy of Xsan software may reproduce this publication for the purpose of learning to use such software. No part of this publication may be reproduced or transmitted for commercial purposes, such as selling copies of this publication or for providing paid for support services. The Apple logo is a trademark of Apple Computer, Inc. , registered in the U. S. [. . . ] 3 Choose Read & Write or Read Only from the Permissions pop-up menu. From the Command Line You can also set read or write access to a storage pool using the cvadmin enable command in Terminal. For more information, see the cvadmin man page or "Viewing or Changing Volume and Storage Pool Settings (cvadmin)" on page 85. Choosing the Types of Files Stored on a Storage Pool You can limit the files that are stored on a particular storage pool to volume journal data and metadata, user data, user data with an affinity for that storage pool, or a combination of these. Journal data and metadata are always stored on the first storage pool in a volume. To choose the data types for a storage pool: 1 In Xsan Admin, select the SAN the storage pool belongs to, click Setup, and click Storage. 2 Double-click the storage pool in the list. 3 Next to Use For, choose the data types to store on the storage pool. 4 Click OK, then click Save. Chapter 3 Managing SAN Storage 49 Setting Storage Pool Stripe Breadth The default stripe breadth value (64 file system blocks) is adequate for storage pools in most SAN volumes. However, you can adjust this value along with the file system block allocation size to tune SAN performance for special applications. For help choosing a stripe breadth, see "Choosing Stripe Breadth for a Storage Pool, " below. Warning: When you change a storage pool's stripe breadth, all data on the storage pool and the volume to which it belongs is lost. To set the stripe breadth: 1 In Xsan Admin, select the SAN the storage pool belongs to, click Setup, and click Storage. 2 Double-click the storage pool in the list. 3 Next to Stripe Breadth, type the new value. Choosing Stripe Breadth for a Storage Pool Xsan uses the storage pool stripe breadth and volume block allocation size together to decide how to write data to a volume. For most SANs, the default values for storage pool stripe breadth and volume block allocation size result in good performance. However, in some cases you might be able to improve read and write performance by adjusting these values to suit a specific application. The stripe breadth of a storage pool is the number of file allocation blocks that are written to a LUN in the pool before moving to the next LUN. To choose an efficient stripe breadth, you need to consider two other factors: · The most efficient data transfer size of the LUN storage device (1 MB for Xserve RAID) · The size of the data blocks written and read by the critical application that uses the volume (as reflected in the block allocation size for the volume) Knowing these values, choose a stripe breadth using this formula: stripe breadth (in blocks) = transfer size (in bytes) / block allocation size (in bytes) For Xserve RAID systems, which have an optimal transfer size of 1 MB, this becomes: stripe breadth = 1048576 / block allocation size If, for example, you are using an application such as Final Cut Pro to move large amounts of video data, choose the largest block allocation size (512KB) and use the equation to find the stripe breadth of 2 blocks. Then, Xsan writes 1 MB of data (two 512KB blocks), in turn, to each LUN in your video storage pool. 50 Chapter 3 Managing SAN Storage The Fibre Channel interface in an Xserve RAID caches up to 1 MB of data before passing the data on to the RAID controller to be written to individual drive modules. So, to minimize the time data spends waiting in the cache, you want to send data to the Xserve RAID 1 MB at a time. Setting the Selection Method for Multiple Connections If there is more than one Fibre Channel connection to the LUNs in a storage pool, you can choose whether Xsan uses one connection until it fails or rotates among the connections. This is called the "multipath method. " To change the multipath method: 1 In Xsan Admin, select the SAN the storage pool belongs to, click Setup, and click Storage. [. . . ] multipath method An Xsan storage pool property. Specifies how Xsan utilizes multiple Fibre Channel paths between clients and storage. Can be set to rotate, which alternates each read or write between available paths for higher performance, or static, which assigns each LUN in a volume alternately to a path at mount time. RAID array A group of physical disks organized and protected by a RAID scheme and presented by hardware or software as a single logical disk. [. . . ]