[Beowulf] hardware RAID versus mdadm versus LVM-striping
landman at scalableinformatics.com
Tue Jan 19 09:43:11 EST 2010
Joe Landman wrote:
> This I cannot tell you, as I don't have a comprehensive list of what
> uses what driver. I'd suggest looking at what drivers it loads for
> disks when it comes up. If dmraid comes up *and* enumerates devices,
> you have a strong probability that it is a fake-raid. This is not to
> say dmraid is bad. Again, its the underlying driver or chipset that we
> often run into problems with.
I should also point out that the presence of dmraid and device
enumeration is still not sufficient for determining whether something is
or is not a fake-raid. To wit
root at crunch:~# df -h /data
Filesystem Size Used Avail Use% Mounted on
4.6T 2.4T 2.2T 53% /data
and /data is on a most assuredly a hardware accelerated RAID. There
were some additional tools I installed with the distribution which also
installed device-mapper. I could turn it off, but then I have some
other bits to work around. It's easier to leave it on.
FWIW: I am no fan of device mapper (the dm part of dmraid). It has
caused us some serious grief in the past (serious grief == data
lossage). Its not in a league with things like rieserfs, ext2, NTFS,
and whatnot ...
When device mapper works correctly (as above) it works fine. A
tautology/Yogi-Berra-ism for sure.
Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics Inc.
email: landman at scalableinformatics.com
web : http://scalableinformatics.com
phone: +1 734 786 8423 x121
fax : +1 866 888 3112
cell : +1 734 612 4615
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