I would NOT do that. You should like the md layer handle all things raid and let lvm do just volume management.
Your under the asumption that they are two different systems.
You're under the assumption that they are not.
http://en.m.wikipedia.org/wiki/Device_mapper
If you want I can forward LXR references to MD and LVM into the device mapper code or LKML references that talk about rewriting MD and LVM for device mapper.
md can make use of dm to get devices for its use but it certainly does not just ask dm to create a raid1 device. md does the actually raiding itself. Not dm.
Md RAID and LVM are both interfaces to the device mapper system which handles the LBA translation, duplication and parity calculation.
Are they? Since when was md and dm the same thing? dm was added after md had had a long presence in the linux kernel...like since linux 2.0
Both MD RAID and LVM were rewritten to use the device mapper interface to mapped block devices back around the arrival of 2.6.
That does not equate to md and dm being the same thing. Like you say, 'TO USE' dm. When did that mean they are the same thing?
I have said it before, but I'll say it again, how much I wish md RAID and LVM would merge to provide a single interface for creation of volume groups that support different RAID levels.
Good luck with that. If key Linux developers diss the zfs approach and vouch for the multi-layer approach, I do not ever see md and dm merging.
I'm not talking ZFS, I'm not talking about merging the file system, just the RAID and logical volume manager which could make designing installers and managing systems simpler.
Good luck taking Neil Brown out then. http://lwn.net/Articles/169142/ and http://lwn.net/Articles/169140/
Get rid of Neil Brown and md will disappear. I think.
To create a raid1+0 array, you first create the mirrors and then you create a striped array that consists of the mirror devices. There is another raid10 module that does its own thing with regards to 'raid10', is not supported by the installer and does not necessarily behave like raid1+0.
Problem is the install program doesn't support setting up RAID10 or layered MD devices.
Oh? I have worked around it before even in the RH9 days. Just go into the shell (Hit F2), create what you want, go back to the installer. Are you so sure that anaconda does not support creating layered md devices? BTW, why are you talking about md devices now? I thought you said md and dm are the same?
You know what, let me try just that today, I have a new install to do, so I'll try pre-creating a RAID10 on install and report back. First I'll try layered MD devices and then I'll try creating a RAID10 md device and we'll see if it can even boot off them.
Let me just point out that I never said you can boot off a raid1+0 device. I only said that you can create a raid1+0 device at install time. /boot will have to be on a raid1 device. The raid1+0 device can be used for other filesystems including root or as a physical volume. Forget raid10, that module is not even available at install time with Centos 4 IIRC. Not sure about Centos 5.
I would definitely avoid layered MD devices as it's more complicated to resolve disk failures.
Huh?
I do not see what part of 'cat /proc/mdstat' will confuse you. It will always report which md device had a problem and it will report which device, be they md devices (rare) or disks.
Having a complex setup is always more error prone to a simpler one. Always.
-_-
Both are still multilayered...just different codepaths/tech. I do not see how lvm is simpler than md.
In my tests an LVM striped across two RAID1 devices gave the exact same performance as a RAID10, but it gave the added benefit of creating LVs with varying stripe segment sizes which is great for varying workloads.
Now that is complicating things. Is the problem in the dm layer or in the md layer...yada, yada
Not really, have multiple software or hardware RAID1s make a VG out of them, then create LVs. One doesn't have to do anything special if it isn't needed, but it's there and simple to do if you need to. Try changing the segment size of an existing software or hardware array when it's already setup.
Yeah, using lvm to stripe is certainly more convenient.
You know you really are an arrogant person that doesn't tolerate anyone disagreeing with them. You are the embodyment of everything people talk about when they talk about the Linux community's elist attitude and I wish you would make at least a small attempt to change your attitude.
How have I been elitist? Did I tell you to get lost like elites like to do? Did I snub you or something? Only you can say that I made assumptions and not you? ???