Articles: Storage

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We’re going to review the new eight-channel SATA II RAID controller from LSI Logic today, the model name MegaRAID 300-8X. This controller not only expands the MegaRAID series quantitatively (it supports eight disks against the ex-senior model’s six) but qualitatively, too. It supports the new SATA II interface and the high-speed PCI-X bus, has a large cache buffer and a battery to power the cache chips in case of emergency server shutdown. All these features make the new controller a top-end product, of course.

The sheer number of disks supported still plays a very important role, however, and the MegaRAID SATA 300-8X makes it possible to build a reliable and fault-tolerant disk subsystem. For example, the MegaRAID SATA 150-6 permitted to build only three RAID1 arrays and we didn’t have a free “hot-spare” drive ready to replace a failed drive in any of the arrays whereas the new controller makes the following configuration possible:

  • Two disks in a RAID1 for the OS and system software
  • Three disks in a RAID5 for the database
  • Two disks in a RAID1 for logging and backup
  • One hot-spare disk

Of course, if you want to store the database on a RAID10 array (and you are sure to want it if the percentage of write operations with the database is going to be higher than… well, you’ll learn the exact number shortly), the system software and the logs are going to share the same array:

  • Three disks in a RAID5 for the system and log
  • Four disks in a RAID10 for the database
  • One hot-spare disk

Earlier, the mainboard’s disk controller had to be employed or another RAID controller had to be added to the server to enable such disk configurations, but now you can do with just a single eight-channel controller with obvious advantages:

  • System reliably improves because there are fewer devices that can potentially fail
  • Server maintenance is simplified
  • The disk subsystem “occupies” only one PCI-X slot

The drawbacks come naturally from the advantages. A centralized disk subsystem is more sensitive to a failure of its keystone, the controller. But we are responsible people and always have a spare controller just in case, aren’t we? :)

Returning to the MegaRAID SATA 300-8X, its functionality grew up also because it now supports the faster PCI-X bus. The new interface is very welcome since the controller supports more disks and the interface bandwidth of each of the disks has doubled. Clocked at 133MHz, PCI-X can theoretically pump through two times more data than the PCI-64 66MHz (1066MB/s against 533MB/s). However, we should note that the peak bandwidth of the bus interface is smaller than the total of the bandwidths of the eight disks (8 x 300MB/s = 2400MB/s).

The amount of the controller’s own cache memory has doubled over the previous-generation models. The MegaRAID SATA 300-8X carries 128 megabytes of DDR SDRAM with ECC. We couldn’t find a mention of the memory speed in the documentation, but judging by the chips marking, we suppose it works at 166MHz, i.e. as DDR333.

The LSliBBU01 battery, if fully charged, can power the cache memory chips for 72 hours on an emergency shutdown of the server. The small letter “i” in the model name means “intelligent” – the battery is compatible with the Smart Battery Data Specification and can report to the controller information about itself and its current charge level.

You can also use a simpler LSIBBU03 battery which is not intelligent and would keep the cache data safe for only 32 hours when the power is off.

The controller supports SATA-150 as well as SATA-300 drives and allows uniting them into RAID arrays of level 0, 1, 10, 5, and 50. It also supports Tagged Command Queuing and Native Command Queuing, so the good old Raptor 2 is not forgotten.

In the next section we’ll have a closer look at the device.

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