Dell PowerVault MD3260 Administrator's Guide - Page 21

Segment Size, Virtual Disk Operations, Virtual Disk Initialization, Consistency Check

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sized databases or any environment that requires high performance and fault tolerance and moderate-to-medium capacity. Segment Size Disk striping enables data to be written across multiple physical disks. Disk striping enhances performance because striped disks are accessed simultaneously. The segment size or stripe element size specifies the size of data in a stripe written to a single disk. The storage array supports stripe element sizes of 8 KB, 16 KB, 32 KB, 64 KB, 128 KB, and 256 KB. The default stripe element size is 128 KB. Stripe width, or depth, refers to the number of disks involved in an array where striping is implemented. For example, a four-disk group with disk striping has a stripe width of four. NOTE: Although disk striping delivers excellent performance, striping alone does not provide data redundancy. Virtual Disk Operations Virtual Disk Initialization Every virtual disk must be initialized. Initialization can be done in the foreground or the background. A maximum of four virtual disks can be initialized concurrently on each RAID controller module. • Background initialization - The storage array executes a background initialization when the virtual disk is created to establish parity, while allowing full host server access to the virtual disks. Background initialization does not run on RAID 0 virtual disks. The background initialization rate is controlled by MD Storage Manager. To change the rate of background initialization, you must stop any existing background initialization. The rate change is implemented when the background initialization restarts automatically. • Foreground Initialization - The storage array executes a background initialization when the virtual disk is created to establish parity, while allowing full host server access to the virtual disks. Background initialization does not run on RAID 0 virtual disks. The background initialization rate is controlled by MD Storage Manager. To change the rate of background initialization, you must stop any existing background initialization. The rate change is implemented when the background initialization restarts automatically. Consistency Check A consistency check verifies the correctness of data in a redundant array (RAID levels 1, 5, 6, and 10). For example, in a system with parity, checking consistency involves computing the data on one physical disk and comparing the results to the contents of the parity physical disk. A consistency check is similar to a background initialization. The difference is that background initialization cannot be started or stopped manually, while consistency check can. NOTE: It is recommended that you run data consistency checks on a redundant array at least once a month. This allows detection and automatic replacement of unreadable sectors. Finding an unreadable sector during a rebuild of a failed physical disk is a serious problem, because the system does not have the redundancy to recover the data. Media Verification Another background task performed by the storage array is media verification of all configured physical disks in a disk group. The storage array uses the Read operation to perform verification on the space configured in virtual disks and the space reserved for the metadata. 21

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sized databases or any environment that requires high performance and fault tolerance and moderate-to-medium
capacity.
Segment Size
Disk striping enables data to be written across multiple physical disks. Disk striping enhances performance because
striped disks are accessed simultaneously.
The segment size or stripe element size specifies the size of data in a stripe written to a single disk. The storage array
supports stripe element sizes of 8 KB, 16 KB, 32 KB, 64 KB, 128 KB, and 256 KB. The default stripe element size is 128 KB.
Stripe width, or depth, refers to the number of disks involved in an array where striping is implemented. For example, a
four-disk group with disk striping has a stripe width of four.
NOTE:
Although disk striping delivers excellent performance, striping alone does not provide data redundancy.
Virtual Disk Operations
Virtual Disk Initialization
Every virtual disk must be initialized. Initialization can be done in the foreground or the background. A maximum of four
virtual disks can be initialized concurrently on each RAID controller module.
•
Background initialization — The storage array executes a background initialization when the virtual disk is
created to establish parity, while allowing full host server access to the virtual disks. Background initialization
does not run on RAID 0 virtual disks. The background initialization rate is controlled by MD Storage Manager. To
change the rate of background initialization, you must stop any existing background initialization. The rate
change is implemented when the background initialization restarts automatically.
•
Foreground Initialization — The storage array executes a background initialization when the virtual disk is
created to establish parity, while allowing full host server access to the virtual disks. Background initialization
does not run on RAID 0 virtual disks. The background initialization rate is controlled by MD Storage Manager. To
change the rate of background initialization, you must stop any existing background initialization. The rate
change is implemented when the background initialization restarts automatically.
Consistency Check
A consistency check verifies the correctness of data in a redundant array (RAID levels 1, 5, 6, and 10). For example, in a
system with parity, checking consistency involves computing the data on one physical disk and comparing the results to
the contents of the parity physical disk.
A consistency check is similar to a background initialization. The difference is that background initialization cannot be
started or stopped manually, while consistency check can.
NOTE:
It is recommended that you run data consistency checks on a redundant array at least once a month. This
allows detection and automatic replacement of unreadable sectors. Finding an unreadable sector during a rebuild
of a failed physical disk is a serious problem, because the system does not have the redundancy to recover the
data.
Media Verification
Another background task performed by the storage array is media verification of all configured physical disks in a disk
group. The storage array uses the Read operation to perform verification on the space configured in virtual disks and the
space reserved for the metadata.
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