On Tue, Mar 12, 2013 at 1:28 PM, Dave Johansen <davejohansen@xxxxxxxxx>wrote:
> On Fri, Mar 8, 2013 at 6:14 AM, SilverTip257 <silvertip257@xxxxxxxxx>
> wrote:
> >
> > On Thu, Mar 7, 2013 at 6:54 PM, Gerry Reno <greno@xxxxxxxxxxx> wrote:
> >
> > > On 03/07/2013 06:52 PM, Les Mikesell wrote:
> > > > On Thu, Mar 7, 2013 at 5:40 PM, John R Pierce <pierce@xxxxxxxxxxxx>
> > > 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.
> 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,
> Dave
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--
---~~.~~---
Mike
// SilverTip257 //
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