Mailinglist Archive: opensuse (982 mails)

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[opensuse] Re: Hard Disk Upgrades
John Andersen wrote:
On 9/11/2014 12:47 PM, Linda Walsh wrote:
It is a solution you get w/o paying extra for a RAID card
but that has *no hardware acceleration*... but the BIOS presents
a RAID0 or RAID1 set as 1 disk for normal interactions.

I believe you will find the hardware acceleration is mythical anyway.
At least that's been my finding.
Compare RAID 5, 6, 50, 60 against the same using linux
mdraid setups. Check your throughput as well as cpu usage.
I think you'll find the mdraid version notably more taxing on
your cpu.
Of course on RAID0/1/10 no cpu is needed to schedule
2 async writes to each mirror and wait for them to complete.

Modern I/O controllers don't write synchronously to single disks,
why would they do so to mirrors?

Again, John Andersen wrote:
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.)
vs. using SW-BIOS RAID, you only see 1 disk for the RAID, you don't see
the separate pieces -- not at boot and and not in /dev.

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.).
If you say so... but SATA only talks to 1 disk/channel unless you use a
SATA multiplexor -- which requires special drivers to work on windows and on linux --
(unlike the SAS expanders, the SATA expanders are cautioned against).

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