Promise Technology EX4650 Choosing Cache Policy, TB Limitation, Logical Drive Size Sector Size

Chapter 7: Technology Background

•Linux operating systems with the 2.6 kernel support 64-bit LBA. For these OSes, always choose the default 512 B sector size.

See “Creating a Logical Drive” on page 93 and “Creating a Logical Drive” on page 159, and “Creating a Disk Array – Advanced Configuration” on page 155.

2 TB Limitation

If your Host PC runs Windows XP (32-bit), and you want to create logical drives larger than 2 TB, you must choose a sector size larger than 512 B when you create the logical drive. The table on the next page 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)

Also see “Ranges of Disk Array Expansion” on page 246.

Choosing Cache Policy

As it is used with SuperTrak, 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 “Creating a Logical Drive” on page 93 and “Creating a Logical Drive” on page 159, and “Creating a Disk Array – Advanced Configuration” on page 155.

•On an existing logical drive. See “Changing Logical Drive Settings” on page 95 or page 168.

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