UNIX for Advanced & Expert Users

Hi,

This will explain things, I think.

But it does give rise to a couple of other questions, the first being how many physical drives are there in the system. If the answer is less than five, you will see degradation in the read and write perfomance as it is likely that behind the hypervisor (in your case VirtualBox) there will be less paths than defined devices.

The second question is are you in fact running VirtualBox on a Physical or within a Virtual Server.

Regards

Dave

1) I have only one physical drive in the system.
2) I am running VirtualBox on a Physical server (host).

Hi,

Unfortunately having only a single drive here is going to skew these figures, to test this properly you'll need multiple physical drives.

There are multiple impacts here - mostly from the hard drive, the seek time and latency will be major contributors as virtual box only creates a contiguous file if you specify that it should preallocate all the disk space. Other than that it will scatter the writes all over the disk if you specify that it should grow the file as required.

I don't think that this is really a suitable way to evaluate the performance of any RAID as it's all on one physical disk.

Regards

Dave

I agree with you. I actually gave it a try because I didn't have any other setup available to test. But in theory (leaving VirtualBox aside, and if I had the actual physical drives available), reads should be ~twice as fast, and writes about as fast as RAID1, am I correct?

Hi,

The RAID10 performance will be faster, but I'm not sure it will be twice as fast. Generally better performance is related to an increase on the number of spindles. There are also benefits to be derived from the committal regime but there can be a certain amount of trial and error, there are a great many factors that influence the performance of a RAID array - that's why there are a great many books and courses on the subject.

Regards

Dave

That depends on what the bottleneck is in whatever configuration you're testing, and how you're testing it.

Hi.

Here is a report on several disk configurations that was done in 2009 using benchmark code bonnie++ (32-bit 2-CPU Athlon box):

Code:

Description-en: Hard drive benchmark suite.
 It is called Bonnie++ because it was based on the Bonnie program.  This
 program also tests performance with creating large numbers of files.

which can be found in the Debian repositories.

Currently I use RAID10 with 4 SATA disks with LVM on top of the RAID on a virtual-machine server. I have not run the bonnie++ benchmarks on that system, but perhaps I will now that I see that there is some interest.

The only reason I would use RAID10 with less than 4 disks is practice (as with setup, etc), not for performance.

Best wishes ... cheers, drl