On Fri, Mar 22, 2013 at 5:16 AM, SilverTip257 <silvertip257 at gmail.com> wrote: > > On Thu, Mar 21, 2013 at 10:04 PM, Dave Johansen > <davejohansen at gmail.com>wrote: > > > On Tue, Mar 12, 2013 at 5:04 PM, SilverTip257 <silvertip257 at gmail.com> > > wrote: > > > > > > On Tue, Mar 12, 2013 at 1:28 PM, Dave Johansen > > > <davejohansen at gmail.com>wrote: > > > > > > > On Fri, Mar 8, 2013 at 6:14 AM, SilverTip257 > > > > <silvertip257 at gmail.com> > > > > wrote: > > > > > > > > > > On Thu, Mar 7, 2013 at 6:54 PM, Gerry Reno <greno at verizon.net> > > wrote: > > > > > > > > > > > On 03/07/2013 06:52 PM, Les Mikesell wrote: > > > > > > > On Thu, Mar 7, 2013 at 5:40 PM, John R Pierce > > > > > > > <pierce at hogranch.com> > > > > > > wrote: > > > > > > >> On 3/7/2013 3:35 PM, Gerry Reno wrote: > > > > > > >>> Dave, I've been using software raid with every type of > > > > > > >>> RedHat > > > > distro > > > > > > RH/CentOS/Fedora for over 10 years without any > > > > > > >>> serious difficulties. I don't quite understand the logic in > > all > > > > these > > > > > > negative statements about software raid on that > > > > > > >>> wiki page. The worst I get into is I have to boot from a > > > > > > >>> bootdisk > > > > if > > > > > > the MBR gets corrupted for any reason. No big > > > > > > >>> deal. Just rerun grub. > > > > > > >> have you been putting /boot on a mdraid? that's what the > > article > > > > > > >> is > > > > > > >> recommending against. > > > > > > > I've put /boot on md raid1 on a lot of machines (always > > > > > > > drives > > > > > > > small > > > > > > > enough to be MBR based) and never had any problem with the > > > > > > > partition > > > > > > > looking enough like a native one for grub to boot it. The > > > > > > > worst > > > > thing > > > > > > > > > > > > > > > > No problems here either - I have had /boot on software raid1 on > > > > > quite > > > > > a > > > > few > > > > > systems past and present. > > > > > > > > > > > > > > > > > I've seen about it is that some machines change their idea of > > bios > > > > > > > > > > > > > > > > If I do have a drive fail, I can frequently hot-remove them and > > > > > hot-add > > > > the > > > > > replacement drive to get it resyncing without powering off. > > > > > > > > > > > > > > > > > disk 0 and 1 when the first one fails, so your grub setup > > > > > > > might > > be > > > > > > > wrong even after you do it on the 2nd disk - and that would be > > the > > > > > > > same with/without raid. As long as you are prepared to boot > > from > > > > > > > a > > > > > > > rescue disk you can fix it easily anyway. > > > > > > > > > > > > > Good point, Les. Rescue disks and bootdisks are key and > > > > > > critical > > > > > > if > > > > > > you're going to use software raid. > > > > > > > > > > > > > > > > > I think we could argue that rescue disks are a necessity > > > > > regardless > > > > > one > > > > is > > > > > using software raid or not. :) > > > > > > > > Thanks for all of the helpful info, and now I have a follow on > > > > question. I have a Dell m6500 that I've been running as a RAID 1 > > > > using > > > > the BIOS RAID on RHEL 5. The issue is that when you switch one of > > > > the > > > > drives, the BIOS renames the RAID and then RHEL 5 doesn't recognize > > > > it > > > > anymore. So here are my questions: > > > > > > > > 1) Has this issue of handling the renaming been resolved in RHEL 6? > > > > (my guess is no) > > > > > > > > > > I've not seen any weird bios naming issues. > > > > It's an Intel Software RAID and whenever either of the drives are > > switched, the system won't boot at all because it says it can't find > > the device. I end up having to boot to a rescue disk and then manually > > edit the init image to get it to boot. > > > > > > > > > > > > 2) Would a software RAID be a better choice than using the BIOS > > > > RAID? > > > > > > > > > > It depends! In another thread on this list someone said they prefer > > > the > > > reliable Linux toolset over the manufacturer tools/RAID controllers. > > > > > > In a way it comes down to what you can afford and what you are > > comfortable > > > with. > > > And then there are chips on the hardware RAID controllers on which the > > > RAID > > > operations are offloaded. > > > > > > > > > > 3) If a software RAID is the better choice, are there going to be an > > > > impact on performance/stability/etc? > > > > > > > > > > Supposedly hardware RAID performs better. I've not done any tests to > > > quantify this statement I've heard others make. > > > > > > Since it's software RAID, the OS will be using a few CPU cycles to > > > handle > > > the softraid. But I'll doubt you'll miss those CPU cycles ... I > > > haven't > > > and I have a mix of hardware raid and software raid systems. In the > > > end > > > that it will come down to drive performance in terms of how many IOPS > > > you > > > can squeeze out of your drives. > > > > > > Make certain to set up checks for your array health and disk health > > > (smartd). If you use hardware raid many controllers don't allow > > > directly > > > accessing the drives with smartctl ... you have to use a vendor > > > binary/utility (or open source one if available). > > > > > > And then there's aligning your hardware RAID boundaries... [0] [1] :) > > > > > > [0] > > > > > > > > > > http://www.mysqlperformanceblog.com/2011/06/09/aligning-io-on-a-hard-disk-raid-the-theory/ > > > [1] > > > > > > > > > > http://www.mysqlperformanceblog.com/2011/12/16/setting-up-xfs-the-simple-edition/ > > > > Thanks to everyone for all the info and help. It sounds like the best > > solution is a software RAID with /boot being a non-RAID partition and > > then being rsynced on to the second drive, so I'll give that a whirl. > > > > Just a bit of emphasis here: > > I've had success with /boot being part of a RAID1 software array and > installing GRUB on the MBR of both disks. That way if the main/first disk > fails the other disk still has GRUB installed and the system will boot if > rebooted. > > RAID1 is viewed as single disks by GRUB. That is it boots off the _first > drive_ -- it is not until the Linux kernel has loaded and mdadm has > assembled the drives that you actually have a RAID1. Since GRUB only > boots > off one drive it is prudent to install GRUB on both disks when set up this > way. > > Putting /boot on a RAID1 software array will save you having to rsync > /boot > to the other drive. And booting to a rescue CD to install GRUB on the new > drive after the primary drive died. The above configuration is some work > up front, but less hassle in the wake of a drive failure. > > Try it on a test system if you don't trust the configuration ... it will > boot. :) > I have this configuration on fifteen or more systems (rough estimate) and > some have been in service for years. That does sound like a simpler solution in the longer term and I'm more concerned with maintenance/use than with the difficulty of setting it up, so I will give this a whirl. Thanks, Dave