Dell PowerVault MD3000 - Manual (Page 22)

Dell™ PowerVault MD3000 and MD3000i Array Tuning Best Practices
December 2008 – Revision A01 Page 22
For a complete list of commands and instructions on using the CLI Performance
Monitor, refer to the Dell™ PowerVault™ Modular Disk Storage Manager CLI
Guide
on http://support.dell.com/manuals.
4.9 Other Array Considerations
4.9.1 Global Media Scan Rate
Use the Tools tab to change/set the Media Scan settings in the MDSM. Global
Media Scan uses CPU cycles and will affect performance if run at an
inappropriate time, for example, during high-use user access or during backups.
Set up and use Global Media Scan for low access logical drives, for example, file
storage drives.
Please note that Dell™ does not recommend disabling media scan or lowering
the media scan interval below 15 days. If Media-Scan is disabled, the risk of
non-predicted failures can increase.
4.9.2 Setting the Virtual Disk-Specific Media Scan
Changing/setting the Media Scan settings in the MDSM is on the Tools tab. To
choose to run Media Scan on specific virtual disk, highlight the appropriate virtual
disk to be scanned, and select the Scan selected virtual disks check box.
4.10 Premium Feature Performance
4.10.1 Getting Optimal Performance from Snapshot
When distributing Snapshot Repositories, locate the repository virtual disks on
separate drives from production virtual disks to isolate the repository writes and
minimize the copy-on-write penalty. When possible, schedule Read I/Os to the
Snapshot virtual disk to off-peak times when I/O activity on the source virtual disk
is lower such as during evening hours.
4.10.2 Getting Optimal Performance from Virtual Disk Copy
The Virtual Disk Copy premium feature uses optimized large blocks to complete
the copy as quickly as possible. Thus Virtual Disk Copy requires little tuning other
than setting the copy priority to the highest level that still allows acceptable host
I/O performance. Virtual Disk Copy performance is affected by other controller
activity and by the RAID level and Virtual Disk parameters of the source virtual
disk and the target virtual disk. A best practice for using Virtual Disk Copy is to
disable all snapshot virtual disks associated with a source virtual disk before
selecting the source virtual disk as a virtual disk copy target volume. Target and
source virtual disks should ideally be resident on separate disk groups when
possible; keeping them on the same disk group raises the potential for lower
performing random I/Os for the copy operation.