Promise Technology 66 Pro RAID Implementation, Largest Storage Capacity Required, Striping RAID

SuperTrak66™ User's Manual Chapter 6

Largest Storage Capacity Required

In the event that the largest capacity possible is required, one of two possible configurations are suggested:

1)Spanning - This method effectively takes advantage of the total capacity of all attached drives. It essentially links all drives together to form one large drive regardless of the size of any individual drive (i.e. a 14.0GB drive and a 16.8GB drive will yield a 30.8GB storage array). This method offers no other RAID performance or data redundant features. It simply offers storage capacity.

2)Striping (RAID 0) - This method may be used with up to four (4) identical drives and may provide an additional performance gain over Spanning. If you connect four 16GB drives , you will get a 64GB drive array.

6.2RAID Implementation

This section describes the advantages and disadvantages of the various RAID levels under particular workloads. This information can be used to select a RAID level appropriate for a system with known performance requirements which do not match any of the application scenarios in section 5.1.

Striping (RAID 0)

Striping is an effective method of gaining performance, but offers no fault tolerance. The measurable performance gain from using a striped array may vary depending on the typical application usage.

For applications which tend to perform random read/writes of varying sizes to the drive, a large stripe block size is recommended. With a large block size, a higher percentage of random read/write I/Os will be completed with just a single physical drive I/O. In such a scenario, four drives striped may provide up to four times the performance in multi-threaded applications versus a single drive.

For applications that tend to perform sequential/streaming read/writes (such as working with large database or project files, or editing audio/video), a small stripe block size is recommended. With a small block size, the extended sequential read/writes will assure that all physical drives are feeding data simultaneously. In such a scenario, four drives striped will provide much higher performance than a single drive. With the same small stripe block size, random multi-threaded read/writes of small-to-medium sized files may exhibit poorer performance when compared with a large block size.

Depending on the typical usage of the array, performance gains are directly affected by the stripe block size. Note that whatever block size you do choose, it will always be a compromise.

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