From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Mandar Joshi" Subject: performance degrade with RAID6 against RAID0 Date: Thu, 21 Aug 2014 00:17:54 +0530 Message-ID: <005101cfbca7$419a3820$c4cea860$@calsoftinc.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: References: In-Reply-To: Content-Language: en-us Sender: linux-raid-owner@vger.kernel.org To: NeilBrown , linux-raid@vger.kernel.org List-Id: linux-raid.ids Hi, =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 I want to know how much p= erformance degrade (if any) is expected when same disks-same config settings are used for RAID0 and RA= ID6. With the help of few mails on this mailing list and information availab= le on opensource, I tuned my disks/raid with which I got following, Linux kernel used: 2.6.32 RHEL6.4 Underlying scsi devices config set at: max_sectors_kb=3D8192, scheduler=3Dnoop (or deadline) Buffered IO using xdd, dd:: block size=3D4MB, all sequential writes IO done directly on md/raid device /dev/mdX 6 disks buffered IO total write speed =3D 1000 MBps i.e. around 165 MBp= s per disk RAID0: 64KB chunk size 6 disks =3D 980 MBps i.e. around 164 MBps per di= sk RAID6: 64KB chunk size 6 (4 + 2) disks with stripe_cache_size =3D 8192, preread_bypass_threshold =3D 8192. No pre-reads seen. Gives=20 340 MBps i.e. around 85 MBps per data disks (4) i.e. around 45-50% drop is seen. Same IO tool and IO settings used for all 3 experiments. In general, Is this much drop expected with RAID6 against same RAID 0 config? If not, Is any configuration setting is missing? If I could drive RAID0 with line speed should I expect same with RAID6 = also. Thanks in advance, Mandar Joshi -- 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