IBM System Storage DS4000, Руководство по оборудованию

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Chapter 4. IBM System Storage DS planning and configuration
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Array configuration
Before you can start using the physical disk space, you must configure it. You divide your
(physical) disk drives into arrays and create one or more logical drives inside each array.
In simple configurations, you can use all of your drive capacity with just one array and create
all of your logical drives in that unique array. However, this presents the following drawbacks:
򐂰 If you experience a (physical) drive failure, the rebuild process affects all logical drives,
and the overall system performance goes down.
򐂰 Read/write operations to different logical drives are still being made to the same set of
physical hard drives.
The array configuration is crucial to performance. You must take into account all the logical
drives inside the array, as all logical drives inside the array will impact the same physical
disks. If you have two logical drives inside an array and they both are high throughput, then
there might be contention for access to the physical drives as large read or write requests are
serviced. It is crucial to know the type of data that each logical drive is used for and try to
balance the load so contention for the physical drives is minimized. Contention is impossible
to eliminate unless the array only contains one logical drive.
Drive types
There are three different disk drive types available for the DS Storage Systems:
򐂰
Fibre Channel (FC) disks (Encryption capable FDE or not)
򐂰 Solid State Drives (SSD)
򐂰 Serial ATA disks (SATA)
RAID arrays can only be created by using the same disk types. Depending the usage planned
for a specific array, you might want to choose the right disk type to optimize the overall
performance.
If your application demands high levels of throughput, then both SATA and FC disk types have
similar performance values.
SSD drives, on the other hand, are much better for I/O intensive applications, but not as good
as FC or SATA for throughput. If your application is critical for I/O operations, then your best
disk selection is SSD, then FC; avoid using SATA drives.
Number of drives
The more physical drives you have per array, the shorter the access time for read and write
I/O operations is. So having many disk drives per array will benefit the transactional
environment, where a high number of I/O operations per second are needed. However, this is
not the same number of drives that the sequential access applications need, so the number of
drives to select per array have to be considered according to the application environment.
Tip: Select the best drive types for your array, depending on your application needs:
򐂰 For I/O demanding applications, use as first choice SSD, then FC, and then SATA.
򐂰 For throughput demanding applications, use FC or SATA as your first options.