>>>> 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? ???