From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Rees Subject: Re: raind-1 resync speed slow down to 50% by the time it finishes Date: Thu, 30 Jul 2009 13:11:20 -0700 Message-ID: <72dbd3150907301311t5abef2fai91cdae154b987d33@mail.gmail.com> References: <20090730073554.GA17665@cthulhu.home.robinhill.me.uk> <20090730101846.GA17332@rap.rap.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20090730101846.GA17332@rap.rap.dk> Sender: linux-raid-owner@vger.kernel.org To: =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids 2009/7/30 Keld J=F8rn Simonsen : > I think raid10,f2 only degrades 10-20 % while raid1 can degrade as mu= ch > as 50 %. For writing it is about the same, given that you use a file > system on top of the raid. Has anyone done any benchmarks of near vs far setups? =46rom what I understand, here's how performance should go for a 2-disk raid10 setup: Streaming/large reads far: Up to 100% faster since reads are striped across both disks Streaming/large reads near: Same as single disk as reads can't be striped across both disks Streaming/large writes far: Slower than single disk, since disks have to seek to write. How much of a hit in performance will depend on chunk size. Streaming/large writes near: Same as single disk. Random/small reads far: Up to 100% faster Random/small reads near: Up to 100% faster Random/small writes far: Same as single disk. Random/small writes near: Same as single disk. So basically, if you have a setup which mostly reads from disk, using a far layout is beneficial, but if you have a setup which does a higher percentage of writes, sticking to a near layout will be faster. I recently set up an 8-disk RAID10 across 8 7200 disks across 3 control= lers. 5 disks are in an external enclosure via eSATA and a PCIe card. 2 disks are using onboard SATA controller 1 disk is using onboard IDE controller I debated whether or not to use near or far, but ultimately stuck with near for two reasons: 1. The array mostly sees write activity, streaming reads aren't that co= mmon. 2. I can only get about 120 MB/s out of the external enclosure because of the PCIe card [1] , so being able to stripe reads wouldn't help get any extra performance out of those disks. -Dave [1] http://ata.wiki.kernel.org/index.php/Hardware,_driver_status#Silico= n_Image_3124 -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html