-------- Original-Nachricht -------- > Datum: Thu, 17 Nov 2011 13:59:26 +0100 > Von: Arne Jansen <sensi...@gmx.net> > An: Thomas Schmidt <schmid...@gmx.de> > CC: linux-btrfs@vger.kernel.org > Betreff: Re: [RFC] improve space utilization on off-sized raid devices
> Right you are. So you want to sacrifice stripe size for space efficiency. > Why don't you just use RAID1? > Instead of reducing the stripe size for the majority of writes, I'd prefer > to allow RAID10 to go down to 2 disks. This should also solve it. Yes, that's my trade. With my patch I still have striping across 6 devices for meta (6-7 for data) which is faster then the 2 raid1 would give me. Since 6 drives allready saturate my bus it's a very good trade in my case. While implementing your "degenerated raid0/10" would somewhat lessen the problem (and fix it for me), it would not fix it in general. But implementing it might is still be a good idea. Consider a 4 dev setup: 3 1TB drives and 1 2TB using -m raid1 -d raid0: 80% capacity striped 4 way. -d single: 100% but no striping. My patch: 100% striped 3 way, a good trade imho. I don't think such a setup is unlikely enough to ignore, a home user will simply buy the drive with the best space/cost whenever he needs space, leading exactly to the described situation. Adding a newly bought 2T drive to my 3x1T setup, only to see that only half of it can be used would really piss me off. Note that if the (optional) first "if" is removed I only reduce width if it is required to reach 100% capacity. At least thats the intention, it might need some tweaking. According to the (hackish) simulator I used to test this, typically the average stripe width sacrificed on setups of 5+ unmatched devices is below 2 -- Empfehlen Sie GMX DSL Ihren Freunden und Bekannten und wir belohnen Sie mit bis zu 50,- Euro! https://freundschaftswerbung.gmx.de -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
