IBM Systems Magazine, Power Systems - AIX digital edition - February/March 2009 - (Page 25)
Tips & Techniques Tactical solutions for Power Systems customers Using File-Backed Virtual SCSI Devices BY JANEL BARFIELD i r t u a l I / O S e r v e r ( V I O S ) v e r s i on 1. 5 introduced file-backed virtual SCSI devices. These virtual SCSI devices serve as disks or optical media devices for clients. These new types of virtual devices provide greater f lexibilit y in assigning storage resources to clients. When correctly configured, they may also provide faster access to virtual disks and faster install and restore for clients. In the case of file-backed virtual disks, clients are presented with a file from the VIOS that it accesses as a SCSI disk. This file resides on an internal disk or a remote physical volume (like a storage-area network, or SAN, volume). With file-backed virtual optical devices, you can store, install and back up media on the VIOS, and make it available to clients. V a migration or overwrite installation, which can impact rootvg filesystems on the VIOS that contain client disks (some of this data may have to be restored from a backup). There are also performance implications because the VIOS process actively uses the disk(s) containing the VIOS rootvg. Performance gains are available when a separate disk adapter is used for client traffic. Creating File-Backed Virtual Disks When using file-backed virtual SCSI disks, you def i ne stor age-pool resou rces on t he V IOS to contain the files that will ser ve as client disks. While the VIOS command-line interface abstracts t he underly ing A I X* Logical Volume Manager (LVM) constructs and commands, understanding how the LVM is used helps you configure virtual d i sk s for t he be st pos sible pe r for ma nce. T he r e lat ion s h ip b e t we e n s tor a ge p ool a nd LV M constructs is shown in Figure 1 (page 26). When defining file-backed virtual disks, first use the mksp or mkvg command from the V IOS command-line interface to define a logical volume (LV) storage pool on the VIOS. An LV storage pool is a volume group in AIX LVM. Defining file-backed storage pools in the VIOS’s rootvg volume group isn’t recommended, due to the potential impact to clients when you perform maintenance on the VIOS. Migrating the VIOS (e.g., from V1.5 to V2.1) requires Creating File-Backed Storage Pools T he next step in prov iding f ile-backed v ir t ual disks is creating file-backed storage pools (or AIX LVs). Currently there’s no way to strategically place file-backed storage pools in LV storage pools to take advantage of potential performance gains. You must use the mksp –fb command from the VIOS command line to create file-backed storage pools, and it doesn’t allow you to control placement of logical volumes in the volume group. However, if you follow the recommendations for creating LV storage pools, this shouldn’t be a significant concern. Once you create a file-backed storage pool, create a file-backed virtual disk for a client. Before this step, create virtual SCSI server and client adapters from the Hardware Management Console (HMC) or the Integrated Virtualization Manager (IVM). Using the mkbdsp command, you create a file the client will use, and the virtual target device that links it to a virtual SCSI server adapter in the VIOS in one step. Specify the name of the file-backed storage pool to use, the size of the file-backed disk, the name of the virtual SCSI server adapter and optionally the name of the file and target device the command creates. The client attached to the ser ver adapter will access the file on the VIOS as a SCSI disk. However, since the access is to a file that may be placed across i b m s y s t e m s m a g.c o m/a i x 25 F E B R U A R Y/ M A R C H 2 0 0 9
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Table of Contents for the Digital Edition of IBM Systems Magazine, Power Systems - AIX digital edition - February/March 2009
IBM Systems Magazine, Power Systems — AIX digital edition - February/March 2009
Table of Contents
Editor's Desk: Cooking Up a Management Solution
Trends: IBM Systems Director Active Energy Manager 4.1 Evolves to Offer Improved Savings and Manageability
Case Study: Wakefern Food Corporation exchanges an aging solution…to accelerate data transfers
Cover Story: Managing It All
Features: The relationship between virtual and physical resources on Power Systems
Tips & Techniques: Using File-Backed Virtual SCSI Devices
Administrator: Managing AIX Updates
Product News
Advertiser Index
Power Systems Perspective: Weathering the Storm
IBM Systems Magazine, Power Systems - AIX digital edition - February/March 2009
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