[linux-lvm] lvm and 'poor mans raid' on heterogenous hard dri ves!

[Steve Wray]

> From: linux-lvm-admin at sistina.com [mailto:linux-lvm-admin at sistina.com]On
>
> striping or concatination?
>
> striping means yes same size spaces, but you can just concatinate which
> simply means adding together. So 12+5+4= 21, you could then mirror against
> the 20 gig in software and only loose 1 gig. Whether the controller is
> bright enough to tell the difference is another matter.

Oh yes I see what you mean now, I meant striping,
it was implied.

Could I concatenate the 12+5+4 into one volume and then stripe that
with the 20? Or would that just be suicidal?
oooh or the 5+4 striped, then stripe that with the 12 then the result
with the 20? Resulting in... mental arithmetic... 36G in total.
:)
Its not a production machine by the way. Mostly its my TV.



>
> Thing
>
> -----Original Message-----
> From: Steve Wray [mailto:steve.wray at paradise.net.nz]
> Sent: Wednesday, 20 February 2002 3:54
> To: linux-lvm at sistina.com
> Subject: [linux-lvm] lvm and 'poor mans raid' on heterogenous hard
> drives!
>
>
> Hmmmm,
> Ok so I have 4 hard drives of very varying capacity
> (20G,12G,5G,4G)
> I have an off-board IDE controller (Promise 66)
>
> I think 'maybe I can take advantage of the IDE
> system and put a drive on each master and stripe them.'
> A hardware RAID card would be suboptimal because
> (as I understand it) the striped volume could
> only be as big as the smallest drive.
>
> So, I set up the drives as;
> hda = 20G
> 	hda1 = 64M and is /boot
> 	hda2 = 1G
> hdc = 12G
> 	hdc1 = 1G
> hde = 5G
> 	hde1 = 1G
> hdg = 4G
> 	hdg1 = 1G
>
> The other partitions are set up for various other volume
> groups and non LVM system partitions.
>
> hda2, hdc1, hde1, hdg1 are added to a VG 'fast'
>
> The other LVM partitions on hdc-g are in a volume group that
> doesn't see much traffic, just storage.
>
> I make logical volumes on fast striped across 4 drives.
> So thats 4 partitions at the beginning of the drives,
> with volumes striped across them.
>
> I expected some performance improvements.
>
> So I get the iozone benchmark and start running it on the system.
> I compare performance of striped volumes with performance of a volume
> purely on hda.
>
> Interestingly, the performance improvement is not dramatic,
> I expected better. The main improvement seems to be that the
> striped volumes do better with larger file sizes and as file size
> increases the striped volume keeps its performance up better.
>
> I'm a newbie at this benchmarking lark, so if anyone wants
> the excel spreadsheets generated from iozone just ask,
> I'd like a second opinion! There are some strange things,
> like when file size gets above 16M performance drops dramatically
> regardless of striped or linear volumes... Maybe its something
> to do with extents?
>
>
>
>
>
>
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