Software VS Hardware Raid
Hi all,
Some of you may remember the previous discussion I started regarding RAID
setups...
Okay... after Russell suggested (and some other ppl) that I try software
raid... I did. All *seemed* nice and fine... until I purposely tried to
foil the setup. The array had 2 disks, raid 1 mirroring between the two.
Both disks identical, and master, on 2 seperate cables.
I tried to simulate a few problems I could forsee happening in future
(from experience)... 1) hard disk fails to spin up properly at boot time,
2) disk errors during usage.
Case 1)
I replaced one of the disks with an old disk with bad blocks and strange
sounding noises coming from it (obviously damaged... it had been dropped
previously). When the motherboard was detecting things, it successfully
detected the drive, but during the part that "lilo: " is supposed to come
up, nothing did. The disk kept grinding and grinding, and eventually asked
for a floppy. I was hoping that the 2nd, working drive in the raid array
would kick in any moment, but that didn't happen. Everything stalled right
there. If the bad drive is put in by itself, after a while the disk is
failed and it tries to boot by floppy. The 2 disks are not on the same
cable btw. The BIOS had the usual settings allowing me to set the boot
order (Floppy first, CDrom next, hard disk 0, then network (no, i can't
put hard disk 1, I wish i could), and finally had "Boot other devices" set
to yes.
My question: if this was hardware RAID 1... would this have happened?
Would the hardware RAID controller recognise the problem, and only stop
briefly, then try the second disk automatically and transparently?
Case 2)
I simulated errors by connecting a flaky IDE cable to one of the drives. I
was hoping the software RAID would either compensate by doing most of it's
reading from the good drive (with a good cable) or labelling the flaky
cable/drive as bad, but instead it started slowing down, and writing to
the array was taking much longer and strange errors starting occurring
during writing.
My question: would hardware raid have handled this situation any better?
And as for Hardware IDE raid, which is better... Promise or HighPoint?
promise seems to be better supported in the kernel, but I'm not so sure.
What happens when (for example) a disk in the array fails? How do you
control the hardware raid so you can control a rebuild? And for Promise,
HighPoint, etc., what are the devices going to be called (/dev/hde? or
maybe /dev/raid/array1?)
Thanks in advance.
(btw. google IS my friend, and I have looked through not only linuxdoc.org
(http://www.linuxdoc.org/HOWTO/Software-RAID-HOWTO-3.html), but also
http://www.thelinuxgurus.org/raid.shtml, http://linas.org/linux/raid.html,
http://www.linuxdoc.org/HOWTO/mini/DPT-Hardware-RAID.html but none seem to
really address IDE Hardware Raid cards in any depth).
Sincerely,
Jason
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