Yes, that's why I was careful to clarify that I was talking about parity RAID. Performance should be fine otherwise.
-- Chuck On Wed, Dec 19, 2012 at 8:26 PM, Hua ZZ Zhang <[email protected]> wrote: > Chuck, David, > > Thanks for your explanation and sharing. > Since RAID 0 doesn't have parity or mirroring to provide low level > redundancy which indicate there's no write penalty, it can improve overall > performance for concurrent IO of multiple disks. > I'm wondering if it make sense to use such kind of RAID without > parity/mirroring to increase R/W performance and leave replication and > distribution to higher level of Swift. > > > > [image: Inactive hide details for Chuck Thier ---2012-12-20 上午 > 12:35:58---Chuck Thier <[email protected]>]Chuck Thier ---2012-12-20 上午 > 12:35:58---Chuck Thier <[email protected]> > > > *Chuck Thier <[email protected]>* > Sent by: [email protected] > > 2012-12-20 上午 12:33 > > > To > > > David Busby <[email protected]>, > > > cc > > > "[email protected]" <[email protected]> > > > Subject > > > Re: [Openstack] [swift] RAID Performance Issue > > > There are a couple of things to think about when using RAID (or more > specifically parity RAID) with swift. > > The first has already been identified in that the workload for swift > is very write heavy with small random IO, which is very bad for most > parity RAID. In our testing, under heavy workloads, the overall RAID > performance would degrade to be as slow as a single drive. > > It is very common for servers to have many hard drives (our first > servers that we did testing with had 24 2T drives). During testing, > RAID rebuilds were looking like they would take 2 weeks or so, which > was not acceptable. While the array was in a degraded state, the > overall performance of that box would suffer dramatically, which would > have ripple effects across the rest of the cluster. > > We tried to make things work well with RAID 5 for quite a while as it > would have made operations easier, and the code simpler since we > wouldn't have had to handle many of the failure scenarios. > > Looking back, having to not rely on RAID has made swift a much more > robust and fault tolerant platform. > > -- > Chuck > > On Wed, Dec 19, 2012 at 4:32 AM, David Busby <[email protected]> wrote: > > Hi Zang, > > > > As JuanFra points out there's not much sense in using Swift on top of > raid > > as swift handel; extending on this RAID introduces a "write penalty" > > (http://theithollow.com/2012/03/21/understanding-raid-penalty/) this in > turn > > leads to performance issues, refer the link for write penalty's per > > configuration. > > > > As I recall (though this was from way back in October 2010) the suggested > > method of deploying swift is onto standalone XFS drives, leaving swift to > > handel the replication and distribution. > > > > > > Cheers > > > > David > > > > > > > > > > > > > > On Wed, Dec 19, 2012 at 9:12 AM, JuanFra Rodriguez Cardoso > > <[email protected]> wrote: > >> > >> Hi Zang: > >> > >> Basically, it makes no sense to use Swift on top of RAID because Swift > >> just delivers replication schema. > >> > >> Regards, > >> JuanFra. > >> > >> 2012/12/19 Hua ZZ Zhang <[email protected]> > >>> > >>> Hi, > >>> > >>> I have read the admin document of Swift and find there's recommendation > >>> of not using RAID 5 or 6 because swift performance degrades quickly > with it. > >>> Can anyone explain why this could happen? If the RAID is done by > hardware > >>> RAID controller, will the performance issue still exist? > >>> Anyone can share such kind of experience of using RAID with Swift? > >>> Appreciated for any suggestion from you. > >>> > >>> -Zhang Hua > >>> > >>> > >>> _______________________________________________ > >>> Mailing list: https://launchpad.net/~openstack > >>> Post to : [email protected] > >>> Unsubscribe : https://launchpad.net/~openstack > >>> More help : https://help.launchpad.net/ListHelp > >>> > >> > >> > >> _______________________________________________ > >> Mailing list: https://launchpad.net/~openstack > >> Post to : [email protected] > >> Unsubscribe : https://launchpad.net/~openstack > >> More help : https://help.launchpad.net/ListHelp > >> > > > > > > _______________________________________________ > > Mailing list: https://launchpad.net/~openstack > > Post to : [email protected] > > Unsubscribe : https://launchpad.net/~openstack > > More help : https://help.launchpad.net/ListHelp > > > > _______________________________________________ > Mailing list: https://launchpad.net/~openstack > Post to : [email protected] > Unsubscribe : https://launchpad.net/~openstack > More help : https://help.launchpad.net/ListHelp > > >
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