[TriLUG] Setting Up RAID-5

[Jason Tower]

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

Kevin Otte wrote:
> On Thu, Dec 07, 2006 at 10:51:50AM -0500, Brian Henning wrote:
>>  - Is RAID-5 in software a bad idea?
> 
> This may be the next vi/emacs.  I prefer software RAID under Linux, and
> here's why:
> 
> - Some hardware RAID cards are actually just interface cards with the actual
> RAID code in the driver.  I like to call this WinRAID, an homage to the old
> WinModems.  This one is fairly easily avoidable though by spending a little
> more money and going with a known brand.
> 
> - Well known on-disk format.  I've heard too many horror stories about
> people flashing the firmware on their RAID cards, only to have one of the
> "upgrades" be a change of the disk format and trash the array.
> 
> - More bang for the buck.  CPU cycles are dirt cheap nowadays.  With the
> screamin' mimi's being cranked out today, you'll barely notice the hit on
> the checksumming.
> 
> There are some compelling reasons to go hardware.  I think Jason Tower has a
> list in a thread a couple months ago (perhaps he'll repost).  Based on both
> sides of the coin, I imagine you'll find the right solution for your
> situation.
> 
> Good luck!
>