RAID Level 55

[jason henson]

Nikolas Britton wrote:
> On 7/16/05, Chuck Swiger <cswiger at mac.com> wrote:
> 
>>Nikolas Britton wrote:
>>
>>>I was reading on wikipedia about RAIDs trying to pass the time and I
>>>was thinking why not have RAID 5+5 or 5+5+5 levels, sure you waste
>>>2/3th's of your space but wouldn't this be a killer setup for a
>>>directory server where fast reads are of the utmost importance?
>>
>>Actually, no.  RAID-5 prioritizes cost and reliability at the expense of
>>performance.  RAID-5 does adequate for read-mostly volumes with big files, and
>>does worst with lots of writes to small files.
> 
> 
> Ok then, a public FTP server... It doesn't matter, when your have a
> 405,000 RPM drive (27 drives * 15k rpm) you can do just about
> anything, but it would excel for data reads and especially random data
> reads.
> 
> 
>>RAID-5,0 or -1,0 would be a much better choice.
>>
>>
>>>Would you add up the transfer rates for each drive to get the total
>>>transfer rate of the array?, if true you could easily saturate a 10
>>>gigabit ethernet connection with a 555 array of IDE or SATA drives.
>>
>>Nope.  Most machines are limited by their PCI bus and chipset to less than
>>1Gb/s of backplace bandwidth, although the higher-end boxes with multiple PCI
>>busses or PCIe will do better.
> 
> 
> Yes I realize that the PCI bus is limited to a maximum of 260MB/s
> (32-bit @ 66MHz) but PCI-X @ 133MHz is 1060MB/s....  Anyways...
> 
> I was just thinking out loud if there would be a useful purpose for
> this type of RAID array, I was bored because I had to wait for
> ethereal to build and then I had to wait till 3am, to do something,
> before I could go to sleep for the night.
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> 
If I am not mistaken the nforce products as well as sis and maybe uli 
have direct connect techonlogies for some peripheral to bypass the pci 
in there chipsets.  All have ide connections (I think) that directly 
hook up to the chipset like this to increase performance.

In the nforce products the ata controllers still appear as pci devices, 
but only to make it easy on the drivers (I am guessing here).  I could 
be wrong on some of these products, but I do think most new chipsets 
keep hard disks off the pci bus.

A stripped raid array will be faster than raid 5.  You only do raid 5 if 
you want to have reliability with many disks and waisting have the disks 
with mirroring.

Have you seen the IRam from gigabyte?  It is not out yet, but you should 
google for it.  Something like sustained 130-133Mb/s on SATA 150.