Re raid SW vs HW , was Okay, this is so not cool..

Matt Clark matt at ymogen.net
Thu Oct 16 11:14:00 CDT 2003


> Jessica_Bull at Dell.com wrote:
>
> > Generally speaking hardware RAID is faster.  But the real deciding factor is
> > the speed of your CPU and the load it is handling.  The amount of memory is
>
> today HW: servers with 2 or 3 GHz processors vs. raid with 100Mhz processor,
> I doubt that SW raid is faster. Unless you are using a board with latest intel
> xcale 400-700Mhz processor.
>
> With hw raid you depend of vendors to correct bugs. SW raid are faster,
> flexibler, cheaper and easier to patch.

No doubt all true if you don't have battery backed cache.  With BB cache writes are almost instantaneous, and no amount of CPU can
give you that.

Also don't forget that HW RAID does use special hardware for parity calculations etc, and may well give you many more channels to
work with.  But again, it's the write-back cache that gives you the big win.

And one more thing, if you do RAID on IDE drives for data safety, you *must* turn off the write caching on the _drive_.

Matt





More information about the Linux-PowerEdge mailing list