Articles: Storage
 

Bookmark and Share

(3) 
Pages: [ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 ]

Database Pattern

In the Database pattern the disk subsystem is processing a stream of requests to read and write 8KB random-address data blocks. The ratio of read to write requests is changing from 0% to 100% with a step of 10% throughout the test while the request queue depth varies from 1 to 256.

You can click these links to view the tabled results:

We won’t show both cycles in the diagrams for the sake of clarity because the difference is negligible.

The only firmware algorithm that works at a request queue of 1 is deferred writing. And it works well enough on the LSI 9260-8i: write requests are cached and the performance scales up together with the total amount of cache memory in the disk subsystem (that of the controller and disks) an array has.

Take note of one curious fact: the RAID50 writes about as fast as (and even somewhat faster than) the RAID5 and much faster than the RAID6. There is nothing really odd about that, though. There is no need for a RAID50 to calculate two checksums simultaneously. One checksum is enough. The minor advantage over the RAID5 can be explained by the fact that data for checksums have to be taken from only half the number of disks. So if you are willing to exchange some degree of security (a RAID6 can survive a failure of any two disks whereas a RAID50 can only survive a failure of two disks if the disks fail in both RAID5s) for an increase in writing performance, RAID50 may be the right option for you.

It is not exactly correct to compare this controller with the LSI 8708EM2 we tested earlier since our OS has changed, but anyway. The new controller is faster at writing. Every type of RAID is faster and the RAID5’s graph is nearly horizontal. The graph of the RAID10 even curls up on the right. What is especially nice, the controller has not lost its ability to effectively search for the luckier disk in a mirror pair. It is through this technique that the RAID10 is ahead of the other arrays at high percentages of reads.

Take note that the RAID50 is still much better at writing than the RAID6 although has no advantage over the RAID5 anymore.

When the queue depth is increased to 256 requests, we see the RAID50 lose its speed at high percentages of reads. While the other arrays yield about the same amount of read operations from eight disks (excepting the RAID10 which is better than the others by choosing the luckier disk in a mirror), the RAID50 is surprisingly slower. Otherwise, everything is very good, and we can see rather high results at writing.

 
Pages: [ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 ]

Discussion

Comments currently: 3
Discussion started: 12/07/09 05:06:58 PM
Latest comment: 01/11/10 06:56:45 AM

View comments

Add your Comment