On Sun, May 3, 2009 11:33 am, Leslie Rhorer wrote: >> First thing is, DO NOT boot from raid5/6. It's pointless anyway. > > I agree. I don't. I think it is very valuable for people to share their experiences of what works and what doesn't. Of what problem situations arise and what solutions seem effective. It is even good to give advice when advice is sought. But to assume that the thing which works best for you will always work for everyone else - or vice versa - is wrong. And people seem to be appearing close to that assumption. > >> Summing up, I don't get, why would anybody really want to boot from >> raid5 >> or 6. > > Well, I can see the reasons, but to my mind they are outweighed by the > problems inherent in doing so and the fact the benefits are minimal. > You are very welcome to share what you see as the inherent problems. But please be aware that others may see benefits that you do not. > With hard drives being so inexpensive, I see no reason not to have > separate > boot drive or mirrored set and data devices. Yes, hard drives are cheaper than they once were. But they still aren't free. And they do consume measurable volume and current. If I happen to have a box which has only got room for 4 drives, then I'm not going to use two of them just for boot, nor am I going to plug in external drives with all the risks associated with them. My own "ideal" would be - simple boot loader in first sector of every drive that loaded a 'second stage' linearly off the early sectors of the disk. - the 'second stage' is a linux kernel plus initramfs which finds the root filesystem loads the final kernel and initramfs, and uses kexec to boot into it. Thus the final stage of the boot loader can understand any filesystem, any raid level, any combination of controllers. The area that stores the second stage would be written rarely, and always written as a whole - no incremental updates. So much of the power of md/raid1 would not be necessary. Having some tool that installed the boot loader and second stage on every bootable device would seem an adequate solution. Whether this space were kept free by traditional partitioning, or by the filesystem or raid or whatever "knowing" to leave the first few meg free is of relatively little interest to me. I can see advantages both ways. While that would be my ideal, I'm quite happy to support other people in experimenting with other approaches. It is by being open to making mistakes and learning from them that we grow. So I still plan to offer a "--reserve-space=2M" option for mdadm to allow the first 2M of each device to not used for raid data. Whether any particular usage of this option is viable or not, is a different question altogether. NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
