Promise Technology VTRAK M210i, Product Manual

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Chapter 7: Technology Background
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Choosing Stripe Size
Stripe Size, also called “Stripe Block Size”, refers to the size of the data blocks
written to, and read from, the physical drives. Stripe Size is specified when you
create a disk array. In order to change the Stripe Size of an existing disk array,
you must delete the disk array and create a new one. You can select Stripe Size
directly when you use the Advanced function to create a disk array. If you use the
Express function to create a disk array, WebPAM PRO selects the Stripe Size
when you choose an Application Type.
The available Stripe Sizes are 64, 128, 256 KB, 512 KB, and 1 MB. 64 KB is the
default. There are two issues to consider when selecting the Stripe Size.
First, you should choose a Stripe Size equal to, or smaller than, the smallest
cache buffer found on any physical drive in the disk array. Selecting a larger
value slows read/write performance because physical drives with smaller cache
buffers need more time for multiple accesses to fill their buffers.
Second, if your data retrieval consists of fixed data blocks, such as with some
database or video applications, then you should choose that size as your Stripe
Size.
If you do not know the cache buffer or fixed data block sizes, Promise suggests
you select 64 KB as your Stripe Size. Generally speaking, email, POS, and
webservers prefer smaller stripe sizes. Video and database applications prefer
larger stripe sizes.
Choosing Sector Size
A sector is the smallest addressable area on a physical disk drive. Sector Size
refers to the size of sector measured by the number of bytes of data it can hold.
The most common sector size is 512 bytes (512 B). A smaller sector size results
in a more efficient use of a disk drive’s capacity. 512 B is the default sector size
for logical drives on VTrak.
Important
For iSCSI, always use a 512-byte sector size.
•
Larger sector sizes are incompatible with the Microsoft iSCSI
initiator.
• Linux systems with the 2.4 kernel do not support variable
sector sizes.
• Linux systems with the 2.6 kernel support 64-bit LBA and do
not need larger sector sizes.