Re: RAID newbie, 1 vs 5, chunk sizes

[Phil Turmel <philip@turmel.org>]

On 06/16/2014 12:14 PM, Nuno Magalhães wrote:
> Thanks for the tips.

> Back to a previous question (assuming i have the drives sorted out first):
> 
> If i create a RAID10 with 3 1TB drives, with --layout=f2, would this
> give me 2TB of space +1TB redundancy? Is this a 1E?
> Using: mdadm --create /dev/md0 --verbose --chunk=128 --level=10
> --layout=f2 --raid-devices=3 /dev/sd[abd]1

No, you'll have 1.5T of available space mirrored by halves.

> If so, what would be the difference to a RAID5:
> mdadm --create /dev/md0 --verbose --chunk=512 --level=5
> --raid-devices=3 /dev/sd[abd]1
> 
> Besides one having redundancy and the other having parity; and that
> RAID5 must compute parity (is that really so horrendously slow
> nowadays?).

You can't fit the redundancy for 2T of data into 1T without some form of
parity raid.

> Other than tiobench, any other benchmarking tools you guys recommend?
> (I've decided to just go slow and test every layer out before moving
> to the next, i.e. 1st RAID, LVM, FSs, Xen, apps.)

I'll leave that one for others. . .  Just don't expect dd to be very useful.

Phil

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