HP Dc5750 WebPAM User Manual - Page 103

Choosing Stripe Block Size, Gigabyte Boundary, Initialization, drives

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Chapter 6: Technology Background Choosing Stripe Block Size The stripe block size value can be set to 32 KB, 64 KB and 128 KB. 64 KB is the default. This selection will directly affect performance. There are two issues to consider when selecting the stripe block size. • Choose a stripe block size equal to or smaller than the smallest cache buffer found on any disk drive in your logical drive. A larger value slows the logical drive down because disk drives with smaller cache buffers need more time for multiple accesses to fill their buffers. • If your data retrieval consists of fixed-size data blocks, such as some database and video applications, choose that data block size as your stripe block size. Generally speaking, email, POS and webservers prefer smaller stripe block sizes. Video and database applications prefer larger stripe block sizes. Gigabyte Boundary The Gigabyte Boundary feature is designed for logical drives in which a drive has failed and the user cannot replace the drive with the same capacity or larger. Instead, the Gigabyte Boundary feature permits the installation of a replacement drive that is slightly smaller (within 1 gigabyte) than the remaining working drive (for example, an 80.5GB drive would be rounded down to 80GB). This can be helpful in the event that a drive fails and an exact replacement model is no longer available. Initialization Initialization is the process of setting all of the data bits on all of the disk drives to zero. This has the effect of erasing any existing data from the drives. This action is especially helpful in creating accurate parity in logical drives with more than four drives. Initialization applies to RAID 1, 5 and 10. When you create one of these logical drives, you can specify Quick or Full Initialization. See "Create a Logical Drive" on page 62. The Full Initialization process begins immediately after the logical drive is created and may take some time to finish, depending on the size of the disk drives in your logical drive. Your logical drive is available while initialization is in progress. 97

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Chapter 6: Technology Background
97
Choosing Stripe Block Size
The stripe block size value can be set to 32 KB, 64 KB and 128 KB.
64 KB is the default. This selection will directly affect performance. There are two
issues to consider when selecting the stripe block size.
•
Choose a stripe block size equal to or smaller than the smallest cache buffer
found on any disk drive in your logical drive. A larger value slows the logical
drive down because disk drives with smaller cache buffers need more time
for multiple accesses to fill their buffers.
•
If your data retrieval consists of fixed-size data blocks, such as some
database and video applications, choose that data block size as your stripe
block size.
Generally speaking, email, POS and webservers prefer smaller stripe block
sizes. Video and database applications prefer larger stripe block sizes.
Gigabyte Boundary
The Gigabyte Boundary feature is designed for logical drives in which a drive has
failed and the user cannot replace the drive with the same capacity or larger.
Instead, the Gigabyte Boundary feature permits the installation of a replacement
drive that is slightly smaller (within 1 gigabyte) than the remaining working drive
(for example, an 80.5GB drive would be rounded down to 80GB). This can be
helpful in the event that a drive fails and an exact replacement model is no longer
available.
Initialization
Initialization is the process of setting all of the data bits on all of the disk drives to
zero. This has the effect of erasing any existing data from the drives. This action
is especially helpful in creating accurate parity in logical drives with more than
four drives.
Initialization applies to RAID 1, 5 and 10. When you create one of these logical
drives, you can specify Quick or Full Initialization. See “Create a Logical Drive”
on page 62.
The Full Initialization process begins immediately after the logical drive is created
and may take some time to finish, depending on the size of the disk drives in your
logical drive. Your logical drive is available while initialization is in progress.