On Fri, Feb 02, 2007 at 12:10:33PM +0100, Pim Bliek wrote: > On 2/1/07, Douglas Allan Tutty <[EMAIL PROTECTED]> wrote: > >On Thu, Feb 01, 2007 at 01:06:54PM -0500, Michael S. Peek wrote: >> > >> I.e. Right now I've got two large arrays. Should I maybe break that > >> down unto just a bunch of disks and then use LVM to group them together > >> (not use hardware RAID at all), or should I break the disks into each > >> bundles of three and make as many small raid5 arrays as I can and then > >> group them under LVM? > >> > >> What's the general consensus on actually using LVM with hardware RAIDs? > > > >Separate the two concepts: > > raid protects you from drive failure > > > > LVM allows you to move partitions from one block device (drive, > > raid array, whatever) to another and to resize those partitions. > > > >So do both. > > > >If you're using hardware raid and one disk starts failing, I would think > >that you would want one port free on your hardware controller where you > >can add a new disk (or leave a hot spare) to allow swapping out a > >failing (but not totally failed) drive without degrading the array by > >pulling the failing drive first. > > > >Since I've never had a hardware raid card, I could be wrong on this. > > > >If I recall correctly, the drive-space efficiency goes up the more > >drives you have in a raid5 array. If you broke it up into 3-drive > >arrays, you'd only have 66% efficiency vs whatever you have now. > > > >I'm assuming that your two large arrays aren't one huge array because of > >using two hardware raid controllers. > > > >Personally, I'd use both arrays as PVs for LVM. Then the LVs can be > >made stripe for better performance (since raid protects you from drive > >failures). > > > >FYI, remember that /boot can't be on lvm. I have mine on a raid1. > > > >I have no idea how to set this up after install if you're wanting / on > >LVM. I did mine during Etch install. > > > >Since you're going to all this trouble, choose a good FS like XFS or > >JFS. > - I have 4 300GB disks in a RAID5 array. On a hardware RAID > controller. This gives me 900 GB space. Secure. If a drive fails, the > array is degraded but my data is safe. Just replace the drive, have > the array rebuilt and you're done. > > - Second layer is LVM. LVM is not there to protect your data. Anyone > who makes you think that, ignore. LVM is there to give you > flexibility. > > - I use this 900GB array as one big pool. I can create LV's on it, > resize them, etc. Also, what I find very nice about LVM: I can give > them logical names. Reads a lot easier than /dev/sda7. > > - If you happen to have a *lot* of disks in multiple hardware RAID5 > arrays, you can use LVM to shuffle around LV's. You can move and LV > from one array to another, as long as they are both part of your VG. > > Anyway, do some reading on LVM in the LVM-Howto. But don't confuse LVM > with RAID. My Advise: keep your RAID array in place, put LVM on top. > Do some thinking on the lay-out of your volumegroups and logical > volumes.
Hi Pim, I think we're in basic agreement. The only difference that I can see between our approaches is that I suggested having a spare port on the hardware raid card to add the new drive before removing a partially-failed drive. IIRC, normal raid5 can only tolerate one failed drive. What happens if a second drive fails totally while you're swapping out a failing one? Doug. -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
