Promise Technology M200p, M500i, M500f, M300p, M500p, M300i, M300f, M200i, M200f Read Cache Policy

Chapter 7: Technology Background

To make use of logical drives greater than 2TB in size, a larger sector size is required. The table below correlates sector size with logical drive capacity.

Logical Drive Size	Sector Size
8 to 16 TB	4096 bytes (4 KB)
4 to 8 TB	2048 bytes (2 KB)
2 to 4 TB	1024 bytes (1 KB)
0 to 2 TB	512 bytes (512 B)

When you create a Disk Array using the Express or Advanced methods, and when you create a Logical Drive, you can specify sector size of 512 B; 1, 2, or 4 KB. 512 B is the default.

In most cases, you should select the smallest sector size that will allow full use of the physical disk drives in your disk array.

Because logical drives can be expanded, you may encounter a situation where the usable capacity of your expanded logical drive is reduced by the addressing issue described above. There are two alternatives:

•Limit your logical drive expansion to within the limits described in the chart.

•Back up your data, then delete your existing logical drive and create a new one with a larger sector size.

Cache Policy

As it is used with VTrak, the term cache refers to any of several kinds of high- speed, volatile memory that hold data moving from your computer to the physical drives or vice-versa. Cache is important because it can read and write data much faster than a physical drive. There are read caches, which hold data as it is read from a physical drive; and write caches, which hold data as it is written to a physical drive.

In order to tune the cache for best performance in different applications, user- adjustable settings are provided. Cache settings are made in conjunction with logical drives:

•When you create a logical drive. See “Create a Logical Drive” on page 135

•On an existing logical drive. See “Logical Drive Settings” on page 144

Read Cache Policy

•Read Cache – The read cache is enabled.

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