Eric Sandeen wrote:
Bill Davidsen wrote:
Eric Sandeen wrote:
Hi, I hope this isn't a FAQ, I did do a little searching first...
I'm looking at using a couple of large disks to mirror a system which
currently has a few different filesystems; I'll use partitions on the
disks to contain the different fileystems.
It looks like I could mirror sda and sdb, and partition the resulting
md_d0. Or, I could partition sda and sdb, and create mirrors md0, md1,
etc from the partitions on the underlying disks.
Is there any technical reason to choose one method vs the other? It
seems to me that perhaps on a system with several active partitions from
the same disk, partitioning a single large raid device might allow
better read balancing?
The reason for going with a partitioned raid is that rebuild after a
failure is easier. The reason for NOT going there at the moment is
discussed in another thread here, in the current kernel the partitions
are not started unless you have an initrd file to make that happen. The
last is performance, if you are using the partitions in different ways,
and some would benefit from performance while others (/boot comes to
mind) need to be simple and reliable, and have minimal requirements for
speed. Having partitions on the drive allows you to use different raid
levels across partitions, to best fit what you do with that data.
Thanks. In my case I'd just have raid-1 on everything, so don't need
that granulatiry... Another drawback in my particular case is that the
Red Hat / Fedora tools don't seem to grok partitioned md, but I can fix
that ;)
Is there any merit to my notion about better read balancing across the
entire disk if it's all one md device?
Not that I can see, but that doesn't mean you're wrong, just that I
can't think of any reason why the same load on the same drives would be
better balanced.
--
Bill Davidsen <davidsen@xxxxxxx>
"Woe unto the statesman who makes war without a reason that will still
be valid when the war is over..." Otto von Bismark
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