[Gllug] Hardware comparisons

[Nix]

On 23 Mar 2007, Richard Jones stated:
> On Fri, Mar 23, 2007 at 06:24:37PM +0000, Alain Williams wrote:
>> * Mirroring. Is this best done by the kernel or through a RAID controller ?
>>   I believe that if the kernel sees 2 drives it will do reads in parallel
>>   (I believe that computers read more often than they write); it is
>>   suggested that using a RAID controller will reduce bus bandwidth (write to
>>   controller once which writes to the disks twice) & so make the machine faster.

This is technically true, but...

> Many years ago now I did tests on this and found that software RAID
> was 5 times faster than hardware RAID (2000-era Pentium IIs vs. ICP
> Vortex cards and a really awful Dell RAID card).

... a lot of alleged `RAID controllers' are actually ordinary disk
controllers and a BIOS and Windows disk driver containing a software
RAID implementation (generally a much worse one than Linux's md layer,
needless to say).

Even for those that are not, you're only going to see speedups if you're
maxing the disks out on writes or running with a severely degraded
RAID-6 array. The bus bandwidth of modern PCI systems is such that you
can max out four or five disks easily before you hit the PCI wall.

-- 
`In the future, company names will be a 32-character hex string.'
  --- Bruce Schneier on the shortage of company names
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