Date: Tue, 25 Dec 2007 04:30:46 +0100 From: "fluffles.net" <bsd@fluffles.net> To: Ivan Voras <ivoras@freebsd.org> Cc: freebsd-fs@freebsd.org, freebsd-hardware@freebsd.org Subject: Re: large disk > 8 TB Message-ID: <47707966.4030309@fluffles.net> In-Reply-To: <fjogtv$sc3$1@ger.gmane.org> References: <475D7866.1070803@hangwithme.com> <475D7D60.4040701@fuckner.net> <fjn195$v18$1@ger.gmane.org> <20071212003235.G54053@3jane.math.ualberta.ca> <fjogtv$sc3$1@ger.gmane.org>
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Ivan Voras wrote: > Barkley Vowk wrote: > > >> It looks like he created a 32bit disk label. He needs to use either the >> raw device, or gpt partitions I think. >> >> Ie. /dev/mdid1 or /dev/mdid1p1 instead of /dev/mdid1s1 >> > > You're right :) > I didn't think of checking that - a wrong assumption at my part. > If you are using partitions on a RAID device, you have to make sure you don't end up with a stripe misalignment. If there is misalignment then you end up requiring 2 I/O requests whereas otherwise 1 I/O request would suffice. Naturally this decreases IO performance (less IOps). To avoid a misalignment you have two options: - not using partitions, but using the raw device like Barkley said - use partitions (GPT or normal) and create one large partition, which starts at offset 1MiB (not MB!) thus 1024*1024 bytes. Note that you probably need to convert this to sectors (512 bytes). If you do option 2 right, then the partition will start at precisely the start of a new stripe block - thus there is no misalignment. You can use offsets like 64KiB and 128KiB but i prefer to use 1MiB since that will work with all stripesizes (up to 1MiB, which is rarely used). Merry christmas to all. :) Regards, Veronica
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