Software RAID question
I've been playing with RAID on my linux box, and I have some questions that
maybe someone can help me with.
This is what I have:
Adaptec 29160N PCI SCSI controller
4 IBM Ultrastar fast wide disks
and I am using software RAID provided in the Linux 2.4.x kernel.
When the machine boots up, the speed of the SCSI bus is set to 40 MB/s. Now my
first question is is that 40MB/s *per disk* or is he whole bus set to 40 MB/s
since the disks are fast wide?
I am asking this cos when I am running the disks in RAID 0, the speed goes up in
increments of 10MB/s as I am adding the disks (10 MB/s per disk, which is
exactly as it should be as I get 10MB/s per single disk when benching it on its
own). But, the speed tops off at 30 MB/s, so I am getting exactly the same results (speed wise) with 3 disks as I am with 4 disks.
I am benching with files large enough to avoid any caching and I have also experimented with block and chunk sizes.
What are your opinions, am I getting the figures I should be getting, or is something wrong?
If you feel that something is wrong can you please point it out to me and also give me your view on how to go about fixing it.