Re: lvm mirror or mdadm mirror or raid 5

On Sat, Sep 01, 2007 at 09:31:03PM -0400, Douglas A. Tutty wrote:
> On Sun, Sep 02, 2007 at 08:44:21AM +1000, Alex Samad wrote:
> > On Sat, Sep 01, 2007 at 09:48:38AM -0400, Douglas A. Tutty wrote:
> > > On Sat, Sep 01, 2007 at 12:16:00PM +1000, Alex Samad wrote:
> > > > raid 1 / raid 1 /boot raid 5 - pv
> > > >
> > > > I have been looking at why not to raid 5 and I would go to raid 10
> > > > but I can only put 3 drives in my machine.
> > > >
> > > > Currently have 3x250G and am looking at getting 3x500G, if I go to
> > > > mdadm raid1, then I have 500G safe 500G unsafe which is not really
> > > > what I want.
>
> > > > 1 big vgroup and lots of lv's some with mirrors and some without ?
> > >
> > > I don't see a mirror option in Etch's LV create.
> >
> > Okay I have lenny but I thought mirroring had been in for a while,
> > from my man lvcreate
> >
> > -m, --mirrors Mirrors
> >
> > I haven't looked at this previously so I might be wrong.
>
> Before Etch came out, when I knew that its installer would be doing LVM,
> I decided that when I moved from Sarge that I'd go with LVM. On Sarge's
> lvcreate, there was a -m --mirrors option. When Etch came out it wasn't
> there. I haven't looked into why not but its not there. To me, its the
> one big thing missing from LMV. I suppose though that if we all start
> mirroring in LVM instead of setting up md, then we'll need an LV version
> of mdadm to email us when a mirror degrades from a failing drive.

This is part of no having played with it, was hoping there would have been a few people who are using it to provide some feedback - yeah its good, nope its bad. Or even some people to say dm-mirror is not as good/fast as mdadm..

Guess when I get my new drives I am going to have to try it. My problem is the upgrade path, I don't have the space to backup somewhere else and reload on fresh disk.......

>
> >
> > >
> > > Here's how I would do it:
> > >
> > > Partition 1: 3-way raid1 64 MB for /boot
> >
> > I usually go for 500M, leaves me lots of room to leave stuff not sure
> > why 3 way though, the spare space on the 3rd drive if i go 2 way i use
> > for tmp or swap or ...
> >

>
> If you don't have swap protected, then a failed drive could crash the
> system. Put the swap on LVM. You could also put / on LVM but I didn't
> suggest that since you seemed to want to keep it to a non-LV.
true
>
> I have two drives, 70 GB each. 3 partitions: md0 for /boot, md1 raid1
> for LVM VG-mirror for the system stuff and then the two third partitions
> for VG-cat for non-mirror protected stuff. /home is on a regular LV,
> /var/tmp is on a striped LV. /tmp is on tmpfs. I'm running amd64 and
> have a 300 M LV for / with ext3 gives 291 MB total and I have 170 MB
> used with 107 free with two kernels and their modules installed.
>
> I suggested that you go with 3-way raid1 since you have three huge
> drives anyway, you wouldn't miss 300 MB. Since its a small box with
> three drives in it, cooling is tight. I would guess that you may have
> an increased risk of drive failure because of it. With 3-way raid1 for
> /boot and either three-way raid1 or a mirrord LV if told to mirror to
> all three drives, your whole system is protected from one drive failure
> and your / and /boot are protected from two drive failures.
>
> > > Partition 2: 3-way raid1 300 MB for /
> > again not sure why the 3 way, currently i give 10G for this
>
> 300 MB for / is pleanty if you put all the usual mount points on
> mirrored LVs.
>
> > nice idea to break up into little pv
> > >
> > > Of course, performance won't be as good as if you had 4 drives so
> > > that you didn't have more than one busy md per drive, but this is a
> > > good compromise.
> > >
> > > Why is it that you can't fit in a 4th drive? Are there only 3 bays?
>
> > its a shuttle case, it only has bays for 2 hard drives, I suppose I
>
> How do you fit in three drives plus a DVD then?
the shuttle version i have has room for 3 internal + 1 dvd, I was saying 1 could remove the dvd and install another drive, but i use the dvd too much

>
> > could remove the dvd drive, but I use it a lot, so 3 is the magic
> > number, and it worked well for me, whilst I was a raid 5 guy, but it I
> > am thinking more back to raid1, but I would like to make the decision
> > to mirror or not at lvcreate time not underneath
> >
> > been playing with some HP eva's and I like being able to set the raid
> > level at the lun level
> >
> >
> > > What about an external bay that operates at SATA speeds; look at
> > > addonics.

i work has a much bigger budget than mine, i was look at 500G samsungs drives for $110 (AUS$), which was a good deal
>
> Doug.
>
>
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