On 05/13/2011 09:49 PM, Christopher White wrote:
On 5/13/11 9:01 PM, Rudy Zijlstra wrote:
Hi Chris,
I've run paritioned MD disks for several years now. I do that on
systems where i use md for the system partitions. One mirror with
partitions for the different system aspects. I prefer that, as it
reflects best the actual physical configuration, and all partitions
will be degraded at the same time when 1 disk develops a problem
(which is unfortunately not the case when you partition the disk and
then mirror the partitions).
As i am a bit lazy and have only limited wish to fight with
BIOS/bootloader conflicts / vagaries, these systems typically boot
from the network (kernel gets loaded from the network, from there
onwards all is on the local disk).
Cheers,
Rudy
Thank you for the information, Rudy,
Your experience of running partitioned MD arrays for years shows that
it is indeed stable. The reason for wanting to skip LVM was that it's
one less performance-penalty layer, one less layer to configure, one
less possible point of failure, etc.
I skip LVM cause for my usage pattern it only gives me an additional
management layer... an additional layer to configure
However, Phil again brings up the main fear that's been nagging me,
and that is that MD's partitioning support receives less love (use)
and therefore risks having bugs that go undiscovered for ages and
(gasp) may even risk corrupting the data. People are just so used to
LVM since MD used to be single-partition only, that
LVM+single-partition MD array is far more mature and far more in use.
MD layer and LVM layer are independently maintained. There regular use
together would trigger eventual bugs quicker though.
My main reason against LVM was the performance penalty, where I had
read that it was in the 1-5% range, but I just did a new search and
saw threads showing that any performance hit claim is outdated and
that LVM2 is extremely efficient. In fact the CPU load didn't seem to
be impacted more than 0.1% or so in the graphs I saw.
By the way, Rudy, as for your boot conflicts and the fact that you
resort to running a network boot, that was only a problem in the past
when bootloaders did not support software RAID. Grub2 supports GPT, MD
arrays with metadata 1.2, and can fully boot from a system (with
/boot) installation located on your MD array. All you'll have to do is
make sure your /boot partition (and the whole system if you want to)
is on a RAID 1 (mirrored) array, and that you install the Grub2
bootloader on every physical disk. This means that it goes:
I know... but i happen to dislike grub2, and my network boot environment
is stable and well maintained.
Grub2 is for me a step backwards. more difficult to configure, and i've
gone back to lilo as main bootloader.
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