VTrak M-Class Product Manual
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 8, 16, 32, 64, 128, 256 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.
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). Depending on its capacity, there can be up to 4,000,000,000 sectors on a single disk drive. The number of sectors is limited by the addressing method of the computer's operating system.
Sector size is important for two reasons. First, data is written to a disk drive in units called blocks. If a data block is smaller than the disk drive's sector size, part of the storage space in the sector goes unused. This is why a smaller sector size results in a more efficient use of a disk drive’s capacity.
Second, while a logical drive can be expanded by adding more physical disk drives, the number of addresses cannot be increased above 4,000,000,000, as noted above. For example, your logical drive has 512 byte sectors, multiplied by 4 billion addresses. The result is 2,048,000,000,000 bytes or 2 terabytes (TB) of data storage capacity. If you simply add more disk drives, your operating system will not recognize the additional capacity and you will not be able to use it.
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