From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jon Nelson" Subject: Re: Linux RAID Partition Offset 63 cylinders / 30% performance hit? Date: Wed, 19 Dec 2007 16:12:40 -0600 Message-ID: References: <476990B4.5050803@ziu.info> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <476990B4.5050803@ziu.info> Content-Disposition: inline Sender: linux-raid-owner@vger.kernel.org Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 12/19/07, Michal Soltys wrote: > Justin Piszcz wrote: > > > > Or is there a better way to do this, does parted handle this situation > > better? > > > > What is the best (and correct) way to calculate stripe-alignment on the > > RAID5 device itself? > > > > > > Does this also apply to Linux/SW RAID5? Or are there any caveats that > > are not taken into account since it is based in SW vs. HW? > > > > --- > > In case of SW or HW raid, when you place raid aware filesystem directly on > it, I don't see any potential poblems > > Also, if md's superblock version/placement actually mattered, it'd be pretty > strange. The space available for actual use - be it partitions or filesystem > directly - should be always nicely aligned. I don't know that for sure though. > > If you use SW partitionable raid, or HW raid with partitions, then you would > have to align it on a chunk boundary manually. Any selfrespecting os > shouldn't complain a partition doesn't start on cylinder boundary these > days. LVM can complicate life a bit too - if you want it's volumes to be > chunk-aligned. That, for me, is the next question - how can one educate LVM about the underlying block device such that logical volumes carved out of that space align properly - many of us have experienced 30% (or so) performance losses for the convenience of LVM (and mighty convenient it is). -- Jon