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Re: lvm mirror or mdadm mirror or raid 5

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.
> > 
> > I am going to stick with the /, /boot raid1 sets.
> > 
> > But I was thinking about setting up the rest of the space as pv's and them 
> > using lvm's dm-mirror to manage the mirroring of space ?  then if I don't want 
> > any redundancy on my space I can lvcreate without dm-mirror.
> > 
> > Any one doing this, I haven't had much experience with dm-mirror.
> > my thoughts were 
> > 
> > 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 

 -m, --mirrors Mirrors

I haven't looked at this previously so I might be wrong.

> 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 ...

> Partition 2: 3-way raid1 300 MB for /
again not sure why the 3 way, currently i give 10G for this

> Partition 3: 1/2 of remainder on each drive
> Partition 4: the other 1/2 of remainder.
> Drives are a,b, and c.
> md0: a1, b1, c1  >> raid1 /boot
> md1: a2, b2, c2  >> raid1 /
> md2: a3, b4      >> raid1, as PV for LVM
> md3: b3, c4      >> raid1, as PV for LVM
> md4: c1, a4	 >> raid1, as PV for LVM
> This way, you can still loose one drive and be safe.  It gives you 750
> GB safe, 0 unsafe.
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 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.
> Doug.
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