Mailinglist Archive: opensuse (3156 mails)

[Russell Jones <russell.jones@xxxxxxxxxxxx>]

Aaron Kulkis wrote:
> > You must be assuming that striping across a RAID is somehow a serial 
> > operation.
> That doesn't matter.  Your assumption that the data blocks
> from several disks can be XOR'ed together, and written
> to one of those disks, and the parity partition on yet
> another disk is FASTER than not doing so is just patently
> ridiculous.
So you think CPUs operates more slowly than disks, Aaron? Or do you 
think you need to read data from a disk every time you write it?
> That doesn't even count the matter of increasing the
> bandwidth usage by a factor of N for N disks in the
> RAID 5 configuration.
Aaron said they are "NOT in parallel". It seems reasonable to infer that 
he thinks they are in serial.
> No, I'm asuming that you're using RAID 5, which
> is what you said.
So what did you mean by this:
> No, they are NOT in parallel.  The are issued sequentially.
> They may overlap (only if you have SCSI, or if all of the
> disks are on different controllers), but they are not in
> parallel.
If they occur at the same time, they are happening in parallel. Not 
synchronised, true, but simultaneous, i.e. parallel, even if the data is 
sent to the disks serially. All that's required is for the bus speed to 
be faster than the write speed and for the drives to have a write cache.
> You're obviously a CS major, not an engineer.
And you're a psychology major? ;-)
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