Gentoo Archives: gentoo-amd64

From: Duncan <1i5t5.duncan@×××.net>
To: gentoo-amd64@l.g.o
Subject: [gentoo-amd64] Re: Root on Raid and LVM - Solved
Date: Tue, 08 Nov 2005 12:49:44
Message-Id: pan.2005.11.08.12.43.34.795152@cox.net
In Reply to: [gentoo-amd64] Re: Root on Raid and LVM - Solved by Edward Middleton
Edward Middleton posted <4368286D.90909@××××××××××××.jp>, excerpted below,
 on Wed, 02 Nov 2005 11:46:05 +0900:

>>It appears most aren't running into this bug, yet the number of bugs >>suggests there's a fair number of users. > This bug will only effect users of root on lvm2 users
BTW, I'm not fully up and working yet, but I've decided to put root directly on (a partitioned) raid6, so it can be directly auto-assembled by the kernel and I won't have to use an initrd/initramfs, as (I believe??) I would if root was on LVM2. (The software raid howto is outdated when it says Linux raid can't be partitioned. The 2.6 kernel handles that just fine, but with different device numbers than the traditional non-partitionable raid.) I got 4-300 gig Seagates -- 1.2 terabyte of raw disk space (plus my existing PATA drive space). One of the reasons I'm not up and running yet is that I double-checked the raw drives by running badblocks -w on each entire drive. That's four patterns, written out one at a time to four drives, 300 gig each, then read back in and verified. 4x4x300 gig = 4.8 terabytes written, 4.8 terabytes read. That took me a couple days! =8^) Fortunately, I didn't feel it much at all, save for the wait, because that was traffic on drives I'm not yet using in production, and while it did run 1 CPU to 100% for the entire period, that was mostly I/O wait, and my other CPU kept up with the normal desktop stuff just fine. Anyway... it was waiting for that, that I realized just how much drive space I now have! =8^) I have the raid6 partitioned three ways, my traditional root and backup-root-snapshot as two partitions with the third being the big one -- to hold the rest of my raid6 volumes in LVM, again, for the additional flexibility. There's enough space on the LVM-on-raid6 partition to keep a working and a snapshot copy of everything there, too, guarding against fat-fingering as well as hard drive failure. (A second copy of everything means very little risk playing with reiser4 or the like, as well! =8^) Right now, I have three raids set up (altho I haven't installed filesystems on them yet), a small raid0 (mirrored) for booting, the majority of the space as the three-way-partitioned raid6 mentioned above, and a raid0 (striped for speed, non-redundant) for semi-volatile storage, the portage tree as it can easily be resynced for recovery, /tmp, etc (no, not /etc! <g>). However, after reading up on LVM and realizing it had built-in striping capabilities, I may kill the raid0 and simply use striped LVM directly on the physical volume partitions underneath. Anyway... it was quite cool to realize the 2.6 kernel handles partitioned raid, now, and with direct boot-time kernel raid assembly, I could run root on raid6 without an initrd/initramfs! As I was dreading the complexity of an initrd solution, I grabbed the opportunity to avoid it and still have a raid-backed root, when I saw it! So, no root on LVM here! -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman in http://www.linuxdevcenter.com/pub/a/linux/2004/12/22/rms_interview.html -- gentoo-amd64@g.o mailing list