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By Root 1383 0

seem ideal to allocate two disks for a RAID-1 to house the system partitions. That leaves three remaining disks that you could use to create a RAID-5, yielding 36 GB of raw storage space. However, that's not much room for database growth, and neither array has a spare disk. Furthermore, the system partitions on the RAID-1 aren't going to use anywhere near the whole 18 GB allocated to that array. It might make a bit more sense to create a five-disk RAID-5, segmenting it into two logical drives: one drive with a couple of gigabytes for system partitions, and the other with the remaining space for the database. That should leave you with roughly 70 GB of space for the MySQL partition, depending on how you split up the logical disks. You could also create a four-disk RAID-5 with a single spare disk. That would also leave you plenty of room to create an efficient logical drive for system partitions and another logical drive with room for database growth.

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Warning

Breaking an array into logical drives does not mean that you can implement different RAID levels on the same set of disks. If you have different performance and redundancy requirements for different filesystems, you need to create separate arrays.

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During normal operation, an unsegmented array appears as a logical drive that spans the entire array.

Controller Disk Spin-up

Before a disk can be accessed, it must be spinning at its nominal RPM. This process usually takes only a few seconds and occurs automatically when power is applied to the system. On systems with a lot of SCSI disks, it is useful to defer spin-up until each I/O channel is scanned. This helps underpowered systems with many disks because disks draw additional power during the spin-up process. ATA disks spin up automatically and offer no user control over their startup behavior.

While SCSI controllers can spin up disks, many drives ship with power-on spin-up enabled. That means the disk will spin up as soon as power is applied. If you want to use the controller's deferred spin-up features, you need to enable controller spin-up on individual disks, which is usually accomplished by installing or removing a jumper on each drive. Consult your hard disk manuals for further details.

Mylex

Mylex has two RAID controller product lines, both SCSI-only and both supported directly by the Linux kernel. The entry-level AcceleRAID line currently features a 100 MHz Intel i960 RISC Processor. The high-end eXtremeRAID series boasts a 233 MHz StrongARM SA 110 Processor. Thus, the main difference between the two product lines is the controller's processing power. Within each product line, cards are differentiated by the number of I/O channels present, as well as the amount of cache memory.

Although each card varies slightly in terms of its hardware, they are all managed with the same BIOS and user-space utilities. I evaluated the AcceleRAID 352, a dual-channel controller, but my experiences should apply, regardless of which Mylex card you decide to purchase. For more information about the hardware differences among the available Mylex controllers, consult the Mylex web site at http://www.mylex.com or the driver's home page at http://www.dandelion.com/Linux/DAC960.html.

The DAC960 Driver

All Mylex cards are supported under the DAC960 driver, written by Leonard Zubkoff. The complete documentation for the driver is included with every kernel (/usr/src/linux/Documentation/README.DAC960). The driver documentation contains a complete compatibility list for Mylex RAID controllers. I recommend referring to this list when purchasing any new controller. If your card is not listed there, you may wish to check the DAC960 driver home page at http://www.dandelion.com/Linux/DAC960.html. As long as your controller shares a firmware revision and processor with a controller that is listed as compatible, you will probably have good results in using any new controllers.

Distribution support

Because the DAC960/DAC1100 driver has been in the kernel for such a long time, most distributions now support