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I'm using 2 HDDs each 1TB in size. I'm going to create MDADM+LVM2 over them. Initially I though about this partition layout:

/dev/sda1 - 1Gb (boot)
/dev/sda2 - 500Gb (md0)
/dev/sda3 - 499Gb (md1)

/dev/sdb1 - 1Gb (boot)
/dev/sdb2 - 500Gb (md0)
/dev/sdb3 - 499Gb (md1)

md0 is going to be raid0 and md1 is going to be raid1

however, I found some info that this would be better to break each drive to more partitions (lets say 10 partitions 100Gb in size each). What's the reason of doing that?

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I tried the 'break the partitions into seperate MD's thing a while ago. (For me at least) the theory was that it was easier to replace md devices (w/ smaller disks) and easier to grow it (section at a time) Heaven help you if you extend your vg onto a device that suddenly goes missing and pokes a hole in your LVM lv's ... but if each PV in the vg is raid-backed, then you have that as a safety net.

One of the drives failed spectacularly in this array (Make sure you check your SMART status), and I was able to migrate the data to a more reliable array.

I think it makes little sense to break the drive to that many partitions, and instead let the softraid handle the striping across the disk.

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Yeah, I'd say mirrored data is better. 500BG is not that big these days. So it would be pretty easy to replace one pv. As for a basic stripe, good luck is I can wish you. – d-_-b Apr 19 '10 at 2:57
Well, honestly I still don't understand the reason of breaking them into 10 smaller partitions, instead of having 2 big ones (one for raid0 and one for raid1). I just see no benefits. With smaller partitions - you can't manipulate with separate md devices (the part of the PV) as you just don't know how does LVM place data on them. So you must manipulate with LVs via snapshots if you wanna move/backup data etc. Regarding PV grow - is that bad if you create your PV using whole large partition? :) Don't think so. – archer Apr 19 '10 at 6:22

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