Mailinglist Archive: opensuse (982 mails)

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Re: [opensuse] Re: Hard Disk Upgrades
On 9/11/2014 6:06 AM, Greg Freemyer wrote:
I disagree, *depending* on what type of RAID you want.
If you want RAID0 or RAID1, my experience with BIOS raid for those 2
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.

My experience has been identical to Greg's, and Software Raid
has been bullet proof.

There is one area that you have to be
aware of if you put /boot on a mirrored (raid1) drive, the system
will always boot from which ever disk your menu.lst says to boot
from even if that is part of a MD raid. If that disk fails
you have to manually switch your menu.lst to the other.
(This is why I avoid /boot on MD raid.)

I've had several fake raid cards and several fake raid mother boards,
and each time, I did around to find the jumper that disables the
fake raid and just use the controllers as separate channels.
(The cheapest of the cheap fake raid cards also fake using multiple
channels, so buyer beware, your WRITES will be done serially, not
in parallel on these cheap cards.).

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