On Apr 7, 2005 1:58 AM, David <[EMAIL PROTECTED]> wrote: > Milan Andric wrote: > > >Newbie is getting a fuzzy signal here. Can someone please confirm that > >using RAID 5 and LVM one cannot grow a filesystem by adding > >a new disk/partition? > > > > > It's never that easy I'm afraid. > > Some terms: > A hard disk has lots of data blocks so it's called a block device. > > LVM creates 'volumes' (cf partitions) on top of multiple block devices. > It doesn't do raid5 so, on it's own it doesn't offer raid5 redundancy. > It's easy to 'grow' lvm volumes. > > md provides a virtual block device by RAIDing other block devices. > It's hard to grow a raid5 md device. > It can be done in only 3 ways (AFAIK): > 1 backup, destroy, rebuild bigger and restore > 2 use raidreconf (not 100% succesful - gulp) > 3 use EVMS (not 100% succesful - but supposedly much better than raidreconf) > > You can grow an lvm on top of a raid5 by creating another raid5 device > and growing the lvm onto it. > > If you just grow the lvm onto another disk as Jim Turpin suggested then > if that single disk fails you lose the entire lvm - thus removing the > benefit of doing raid5 anyway. > > Finally, there is a complex idea suggested by Dan Christensen: > > Create multiple partitions on each device: > sda1,sda2,sda3,sda4 > sdb1,sdb2,sdb3,sdb4 > etc > > create 1 raid5 device for each partition > md0=sda1+sdb1+sdc1 > md1=sda2+sdb2+sdc2 > > finally lvm all these together. > > now to add a drive you must: > * add a backup device to the lvm > for each md device > * lvm move the blocks of 1 md device to a backup device > * remove md device from lvm > * destroy + rebuild the md device > * add back to lvm > * lvm move the blocks of the backup device > * remove backup device from lvm > > So, in summary, you *can* grow a RAID5 device - but it's hard. > If you think you will want to grow it I'd suggest starting with EVMS - > it's not that hard to use if you spend some time reading their docs. > Dan's solution (proper credit!) is probably the safest but is time > consuming and possibly human-error prone. > > David >
David, This doesn't look to bad at all after you defined the steps. then again, i'm sure lvm/raid hell will manifest during implementation, but i'm used to that. i think i will try to implement this rather than use yet another tool ... thanks! -- Milan _______________________________________________ mythtv-users mailing list [email protected] http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
