[TriLUG] Setting Up RAID-5

[Jim Ray]

Actually, the hard disks we use cost more than a whole PC (15,000 rpm SCSI)
and ditto for the controller:
http://www.neuse.net/products/server

To get HW RAID5 plus hot spare, HW adds up quit a bit for 4 of those bad
boys.

Regards,

Jim

Jim Ray, President
Neuse River Networks
tel: 919-838-1672 cell: 919-606-1772
http://www.Neuse.Net

Neuse River Networks 


> -----Original Message-----
> From: trilug-bounces at trilug.org [mailto:trilug-bounces at trilug.org] On
Behalf Of
> Josh Vickery
> Sent: Friday, December 08, 2006 9:39 AM
> To: Triangle Linux Users Group discussion list
> Subject: Re: [TriLUG] Setting Up RAID-5
> 
> CPU power may be cheap, but unless I'm mistaken, hard drives are even
> cheaper.  Have you considered multiple raid 1 arrays instead of a
> single raid 5?  The CPU overhead should be lower at the expense of
> less disk space.  It would also probably present the easiest recovery
> situation, since any single disk in the collection would be usable all
> by itself.
> 
> Josh
> 
> On 12/8/06, Matt Bidwell <bidwell at dead-city.org> wrote:
> > Jason Tower wrote:
> > > i'm sure someone can find my old post(s), but there are three major
> > > problems with software raid:
> > >
> > > 1. the bootloader is installed on the MBR of the first disk only.  if
> > > that disk goes bye bye you're in trouble.  sure, you can install
> > > lilo/grub on multiple MBRs but that's a pita and an inelegant
solution.
> > >
> > > 2. some sata chipsets flat out don't work with software raid 5, they
> > > will crash the system hard either during initialization or under heavy
> > > i/o.  i've personally seen this happen on no less than three totally
> > > different systems with multiple distros.
> > >
> > > 3. if a disk dies suddenly, the system is gonna crash regardless of
raid
> > > because the kernel can no longer communicate with /dev/sdx, it just
> > > disappears.  go ahead, set up software raid with hot swap disks then
> > > yank one out while the system is running, see what happens.  the data
> > > itself is probably ok (you'll have a degraded array upon reboot) but
> > > availability is shot.  plus your fstab may no longer be accurate once
a
> > > disk is removed.
> > >
> > > there are probably workaround for these issues, or if they don't
bother
> > > you then knock yourself out with software raid.  i use it myself if
> > > circumstances justify it.  but i've built enough systems to know that
> > > hardware raid exists for a reason.  if you want to do the job right
get
> > > a 3ware card and sleep peacefully.
> > >
> > > jason
> > Jason,
> > As per number one, here is how you write to /dev/md0, /dev/hda and
> > /dev/hdc in lilo.  It's straight from the software raid docs.
> >
> > boot=/dev/md0
> > root=/dev/md0
> > #this writes the boot signatures to either disk.
> > raid-extra-boot=/dev/hda,/dev/hdc
> > image=/vmlinuz
> > label=RAID
> > read-only
> >
> > As far as whether to do raid5 in software, I haven't done it.
> > I do trust mdadm to do raid1.
> >
> > Matt
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