Re: [gentoo-user] dmraid, mdraid, lvm, btrfs, what?

[Michael Mol]

On Tue, Nov 29, 2011 at 2:07 AM, Florian Philipp <lists@×××××××××××.net> wrote:
> Am 29.11.2011 05:10, schrieb Michael Mol:
>> I've got four 750GB drives in addition to the installed system drive.
>>
>> I'd like to aggregate them and split them into a few volumes. My first
>> inclination would be to raid them and drop lvm on top.  I know lvm well
>> enough, but I don't remember md that well.
>>
>> Since I don't recall md well, and this isn't urgent, I figure I can look
>> at the options.
>>
>> The obvious ones appear tobe mdraid, dmraid and btrfs. I'm not sure I'm
>> interested in btrfs until it's got a fsck that will repair errors, but
>> I'm looking forward to it once it's ready.
>>
>> Any options I missed? What are the advantages and disadvantages?
>>
>> ZZ
>>
>
> Sounds good so far. Of course, you only need mdraid OR dmraid (md
> recommended).

dmraid looks rather new on the block. Or, at least, I've been more
aware of md than dm over the years. What's its purpose, as compared to
dmraid? Why is mdraid recommended over it?

> What kind of RAID level do you want to use, 10 or 5? You
> can also split it: Use a smaller RAID 10 for performance-critical
> partitions like /usr and the more space-efficient RAID 5 for bulk like
> videos. You can handle this with one LVM volume group consisting of two
> physical volumes. Then you can decide on a per-logical-volume basis
> where it should allocate space and also migrate LVs between the two PVs.

Since I've got four disks for the pool, I was thinking raid10 with lvm
on top, and a single lvm pv above that.

> Another thing you can think of is whether you want encryption. I've done
> this for my laptop. The usual setup would by md->lvm->crypt. I've done
> it crypt->lvm (an LVM physical volume on top of an encrypted partition).
> This way, I only need to enter the password once. You can enforce a
> specific order between lvm, md and dmcrypt by putting stuff like this in
> /etc/rc.conf:
> rc_dmcrypt_before="lvm"
> rc_dmcrypt_after="udev"

Really not interested in encryption for this box. No need.

-- 
:wq