| Matthew Rosewarne on 26 May 2007 20:56:37 -0000 |
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On Saturday 26 May 2007 13:03, Doug Crompton wrote: > Using Raid 1, lets assume SW raid, and having the following partitiions - > > /boot, /root, /swap, /usr, /home, /lib, and maybe /opt (does Debian use > /opt?) how would one setup raid? > > Does/should swap get included? Do all other partitions get included? > Doesn't the system have to boot outside of raid before in recognizes a > raid partition? To put this thread to rest, let's walk through the process. I use raid 1 with LVM on a number of servers and it's quite easy to set up. It's really not as complex as you make it out to be. *I'll assume here that your drives are identical, not that it matters much. So, imagine now that you're in the Debian installer, when asked, choose to partition manually. You're now looking at the partitioner... 1. Simple setup If you only plan on having one big partition for "/" (similar to what you were doing on Windows), there's no need for LVM and the rest. That said, LVM is wonderful; I never set up machines without it anymore, On each drive, make one swap partition, later on these should be set to the same priority in "/etc/fstab", so the kernel will interleave them (somewhat similar to a RAID 0 setup). The rest of each disk should be another partition to hold the RAID 1, make sure these partitions are set to be bootable. Now choose to configure software RAID, and make a new RAID 1 device with the two RAID partitions. The software RAID device will now show up in the partitioner, format it with your filesystem of choice, and use it as "/". 2. LVM setup If you want to have multiple partitions and swap all mirrored on RAID, you need to use LVM. A. Boot On each drive, create a primary partition, these only need to be big enough to hold the files needed to boot (bootloader, kernel, initramfs), so 25-35 MB should be fine. Use these partitions for software RAID and set them to be bootable. Now choose to configure software RAID, and make a new RAID 1 device from these two small partitions. A software RAID device will now show up in the partitioner. Format this RAID device with ext3, use it as "/boot". Why make this a RAID? Well it lets the system write the boot files to both disks, but the bootloader (which doesn't understand RAID) will just use one of the partitions directly, which is fine since it doesn't write anything. B. Swap You have two options for your swap, you can either lump them in with the rest of your partitions in the LVM, or you can keep them separate. The only reason to keep them separate is if you want them *not* to be mirrored, so you have twice the amount of swap space. If you do keep them separate, you should have the kernel interleave them (somewhat similar to a RAID 0 setup) by setting them to the same priority in "/etc/fstab" later on. If you're keeping them separate, add a swap partition now on each drive. *LVM doesn't make any real difference in the speed of swap, the general rule is that if your machine regularly needs to swap heavily for its usual tasks, then buy more memory. C. LVM The rest of each disk should be one big partition, used for software RAID. Now choose to configure software RAID and make a new RAID 1 device with these partitions. The software RAID device will now show up in the partitioner, use it for LVM. Now choose to configure LVM. Make a new volume group with that software RAID device; I usually call mine vg0, vg1, and so on, but you can call it whatever you like. Now add logical volumes for "/", "/home", "/var", and whatever else (and swap if you decided not to keep it separate). On a desktop machine, I usually just make a logical volume for "/" that is somewhere around 10GB (depending on how much I want to install), and a logical volume for "/home" (so if I overstuff my home directory, the rest of the system won't run out of space). Often I will leave 1 or 2 GB of free space on the volume group, in case I find I need to increase the size of one of the logical volumes later on. > What is confusing to me is that in my Intel MB driven raid the whole drive > is part of the array. As far as the BIOS is concerned it is looking at one > drive. In Linux, using SW raid, would not one drive have to boot linux and > then the raid array is established? If this were the case then it is not > truely raid because if that one drive failed it would not boot. Well, the "RAID" on your motherboard is fake, as others have pointed out. All the work is done in software by the Windows driver, just like the nefarious winmodems of old. You should disable the "RAID" feature in the BIOS (it's worthless) and use Linux's software raid instead, which is probably faster and certainly more disaster-proof. %!PS: RAID is *NOT* a substitute for backup!!! RAID is simply for fault-tolerance, so that your machine can stay up in the event of hard disk failure. If you're relying on RAID to save your data, you're going to get a very unpleasant surprise. %!PPS: Please do not go on long ranting tirades on how Linux is not ready for "the masses" if your reasoning is something like RAID, which "the masses" would never conceivably have to deal with. Advanced matters such as RAID are only ever handled by expert users or OEMs, never by your grandma. Attachment:
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