Dell POWERVAULT MD3600F - Manual (Page 50)

50 Planning: MD3600f Series Storage Array Terms and Concepts
Disk Group Operations
RAID Level Migration
You can migrate from one RAID level to another depending on your
requirements. For example, fault-tolerant characteristics can be added to a
stripe set (RAID 0) by converting it to a RAID 5 set. MDSM provides
information about RAID attributes to assist you in selecting the appropriate
RAID level. You can perform a RAID level migration while the system is still
running and without rebooting, which maintains data availability.
Segment Size Migration
Segment size refers to the amount of data (in KB) that the storage array writes on
a single physical disk in a virtual disk before writing data on the next physical disk.
Valid values for the segment size are 8 KB, 16 KB, 32 KB, 64 KB, 128 KB, 256
KB, and 512 KB.
Dynamic segment size migration enables the segment size of a given virtual disk
to be changed. A default segment size is set when the virtual disk is created, based
on such factors as the RAID level and expected usage. You can change the default
value (128 KB) if segment size usage does not match your needs.
When considering a segment-size change, two scenarios illustrate different
approaches to the limitations:
• If I/O activity stretches beyond the segment size, you can increase it to
reduce the number of disks required for a single I/O. Using a single physical
disk for a single request frees disks to service other requests, especially
when you have multiple users accessing a database or storage environment.
• If you use the virtual disk in a single-user, large I/O environment (such as
for multimedia application storage), performance can be optimized when
a single I/O request is serviced with a single data stripe (the segment size
multiplied by the number of physical disks in the disk group used for data
storage). In this case, multiple disks are used for the same request, but
each disk is only accessed once.
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