[Gllug] re: software vs hardware RAID

[t.clarke]

Can't I have more than a superficial understanding of this  - so while
the 'thread' is current maybe someone can explain better.

My impression is that hardware controller cards are configured prior to O-S
installation using their 'bios' functions (much the sme as a SCSI controller
is configured), so that a number of physical discs are simply presented to the
operating system(s) as one or more logical discs. Thus, the o-s need have no
knowledge of the underlying hardware and simply writes/reads to the logical
disc(s) it sees; relying on the hardware controller to do the actual work
or mirroring/striping or whatever.   This means no extra work for the o-s.

On the other hand, I presume software raid requires the o-s to do all the hard
work, including scheduling and performing two writes for the price-of-one
when mirroring is done, striping etc etc when other levels of raid are done;
all of which would seem to impose extra load on the system.

So, seems to me, as previously stated by Martin, that if you really NEED raid,
go for the hardware variety !  Personally, I reckon except for systems that
absolutely HAVE to be up all the time, modern discs are sufficiently reliable
to make raid a luxury which can be done without.  Of course, I could be tempting
providence ....... :-)

Tim

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