From mboxrd@z Thu Jan 1 00:00:00 1970 From: david@lang.hm Subject: Re: limits on raid Date: Sun, 17 Jun 2007 13:46:47 -0700 (PDT) Message-ID: References: <18034.479.256870.600360@notabene.brown> <18034.3676.477575.490448@notabene.brown> <20070616020320.GB2002@animx.eu.org> <18035.23867.576212.859440@notabene.brown> <20070616140857.GA4206@animx.eu.org> <20070617132809.GB7806@animx.eu.org> <20070617193025.GA8770@animx.eu.org> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: dean gaudet Cc: Wakko Warner , Neil Brown , linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org List-Id: linux-raid.ids On Sun, 17 Jun 2007, dean gaudet wrote: > On Sun, 17 Jun 2007, Wakko Warner wrote: > >> What benefit would I gain by using an external journel and how big would it >> need to be? > > i don't know how big the journal needs to be... i'm limited by xfs' > maximum journal size of 128MiB. > > i don't have much benchmark data -- but here are some rough notes i took > when i was evaluating a umem NVRAM card. since the pata disks in the > raid1 have write caching enabled it's somewhat of an unfair comparison, > but the important info is the 88 seconds for internal journal vs. 81 > seconds for external journal. if you turn on disk write caching the difference will be much larger. > -dean > > time sh -c 'tar xf /var/tmp/linux-2.6.20.tar; sync' I know that sync will force everything to get as far as the journal, will it force the journal to be flushed? David Lang > > xfs journal raid5 bitmap times > internal none 0.18s user 2.14s system 2% cpu 1:27.95 total > internal internal 0.16s user 2.16s system 1% cpu 2:01.12 total > raid1 none 0.07s user 2.02s system 2% cpu 1:20.62 total > raid1 internal 0.14s user 2.01s system 1% cpu 1:55.18 total > raid1 raid1 0.14s user 2.03s system 2% cpu 1:20.61 total > umem none 0.13s user 2.07s system 2% cpu 1:20.77 total > umem internal 0.15s user 2.16s system 2% cpu 1:51.28 total > umem umem 0.12s user 2.13s system 2% cpu 1:20.50 total > > > raid5: > - 4x seagate 7200.10 400GB on marvell MV88SX6081 > - mdadm --create --level=5 --raid-devices=4 /dev/md4 /dev/sd[abcd]1 > > raid1: > - 2x maxtor 6Y200P0 on 3ware 7504 > - two 128MiB partitions starting at cyl 1 > - mdadm --create --level=1 --raid-disks=2 --auto=yes --assume-clean /dev/md1 /dev/sd[fg]1 > - mdadm --create --level=1 --raid-disks=2 --auto=yes --assume-clean /dev/md2 /dev/sd[fg]2 > - md1 is used for external xfs journal > - md2 has an ext3 filesystem for the external md4 bitmap > > xfs: > - mkfs.xfs issued before each run using the defaults (aside from -l logdev=/dev/md1) > - mount -o noatime,nodiratime[,logdev=/dev/md1] > > umem: > - 512MiB Micro Memory MM-5415CN > - 2 partitions similar to the raid1 setup >