Mailinglist Archive: opensuse (982 mails)

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Re: [opensuse] Re: Hard Disk Upgrades
On September 11, 2014 3:53:01 AM EDT, Linda Walsh <suse@xxxxxxxxx> wrote:
Greg Freemyer wrote:
On Wed, Sep 10, 2014 at 5:56 PM, Paul Groves
<paul.groves.787@xxxxxxxxx> wrote:

I have no clue what to do for the RAID. My MoBo supports RAID,
should I use
this functionality or set up a software RAID with opensuse?


That's the first thing you need to decide.

Is your MoBo raid real hardware raid or fake raid?


http://serverfault.com/questions/9244/how-do-i-differentiate-fake-raid-from-real-raid

If fake raid, I would ONLY use it if I needed to be windows
compatible. ie. You need to setup a dual boot windows/opensuse
setup.

----
I disagree, *depending* on what type of RAID you want.
If you want RAID0 or RAID1, my experience with BIOS raid for those 2
types
is that is more versatile, reliable and software transparent.
Since you want RAID1, assuming you are talking SATA or SAS, both
disks can be written-to at the same time by the controller and it will
look like a single disk to windows and linux (and any other OS).

You and I have had different experiences. The most obvious is your
statement about Linux seeing a fakeraid as a single disk. With the
fakeraid I've attempted to use, Linux sees each disk and has to be
made to recognize the fakeraid exists and read the raid config out of
the bios, then take the responsibility of managing the disks just as
it does with software raid.

Fyi: fake raid works by implementing custom firmware in the bios I/o
interface used during boot. Thus Windows and Linux only see a single
drive during the boot process, but for Linux as soon as the normal
ATA/scsi drivers kick in the bios is bypassed and the kernel has to
manage the raid array itself. dmraid (as opposed to MD raid or
mdraid) is the Linux package that is responsible for reading the
config out of the bios and setting up the Linux kernel to manage the
disks correctly.

Due to that, dmraid has to have knowledge of each type of fakeraid
controller and is more likely to have bugs/missing support.

md raid (pure software raid) on the other hand only has to interpret
its own data structures, so there is more flexibility.

You seem to be talking about hardware raid which uses neither dmraid
nor mdraid. I agree hardware raid in general is the best, but it
normally comes with a decent price tag. The cheapest 2-disk hardware
raid 1 controller I've bought was over $100 for just the card.

I've seen and had linux SW RAID5 (as well as HW), and with the same
power and software interruptions, the SWRAID was more vulnerable to
hard
corruptions. W/SW RAID, you can't have a battery-backed up ram that
will
write to the disk when the OS comes up -- because the memory will be
purged.

To my knowledge, battery-backed up ram is a unique feature of true
hardware raid. Your mentioning it continues to make me wonder if we
are talking about the same thing.

Have you ever used dmraid? (again, that is different than md, mdadm, etc.)

Greg
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