On Tue, Jun 2, 2009 at 6:58 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > On Tue, Jun 2, 2009 at 1:11 PM, Jeff Garzik <jeff@xxxxxxxxxx> wrote: >> Neil Brown wrote: >>> >>> I am pleased to (finally) announce the availability of >>> mdadm version 3.0 >>> >>> It is available at the usual places: >>> countrycode=xx. >>> http://www.${countrycode}kernel.org/pub/linux/utils/raid/mdadm/ >>> and via git at >>> git://neil.brown.name/mdadm >>> http://neil.brown.name/git?p=mdadm >>> >>> >>> This is a major new version and as such should be treated with some >>> caution. However it has seen substantial testing and is considerred >>> to be ready for wide use. >>> >>> >>> The significant change which justifies the new major version number is >>> that mdadm can now handle metadata updates entirely in userspace. >>> This allows mdadm to support metadata formats that the kernel knows >>> nothing about. >>> >>> Currently two such metadata formats are supported: >>> - DDF - The SNIA standard format >>> - Intel Matrix - The metadata used by recent Intel ICH controlers. >> >> This seems pretty awful from a support standpoint: dmraid has been the sole >> provider of support for vendor-proprietary up until this point. > > This bares similarities with the early difficulties of selecting > between ide and libata. > >> Now Linux users -- and distro installers -- must choose between software >> RAID stack "MD" and software RAID stack "DM". That choice is made _not_ >> based on features, but on knowing the underlying RAID metadata format that >> is required, and what features you need out of it. >> >> dmraid already supports >> - Intel RAID format, touched by Intel as recently as 2007 >> - DDF, the SNIA standard format >> >> This obviously generates some relevant questions... >> >> 1) Why? This obviously duplicates existing effort and code. The only >> compelling reason I see is RAID5 support, which DM lacks IIRC -- but the >> huge issue of user support and duplicated code remains. > > The MD raid5 code has been upstream since forever and already has > features like online capacity expansion. There is also > infrastructure, upstream, for online raid level migration. > >> 2) Adding container-like handling obviously moves MD in the direction of DM. >> Does that imply someone will be looking at integrating the two codebases, >> or will this begin to implement features also found in DM's codebase? > > I made a proof-of-concept investigation of what it would take to > activate all dmraid arrays (any metadata format, any raid level) with > MD. The result, dm2md [1], did not stimulate much in the way of > conversation. > > A pluggable architecture for a write-intent log seems to be the only > piece that does not have a current equivalent in MD. However, the > 'bitmap' infrastructure covers most needs. I think unifying on a > write-intent logging infrastructure is a good place to start working > together. > >> 3) What is the status of distro integration efforts? I wager the distro >> installer guys will grumble at having to choose among duplicated RAID code >> and formats. > > There has been some grumbling, but the benefits of using one > linux-raid infrastructure for md-metadata and vendor metadata is > appealing. mdadm-3.0 also makes a serious effort to be more agreeable > with udev and incremental discovery. So hopefully this makes mdadm > easier to handle in the installer. > >> 4) What is the plan for handling existing Intel RAID users (e.g. dmraid + >> Intel RAID)? Has Intel been contacted about dmraid issues? What does Intel >> think about this lovely user confusion shoved into their laps? > > The confusion was the other way round. We were faced with how to > achieve long term feature parity of our raid solution across OS's and > the community presented us with two directions DM and MD. The > decision was made to support and maintain dmraid for existing > deployments while basing future development on extending the MD stack, > because it gave some feature advantages out of the gate. So, there is > support for both and new development will focus on MD. > >> 5) Have the dmraid maintainer and DM folks been queried, given that you are >> duplicating their functionality via Intel and DDF RAID formats? What was >> their response, what issues were raised and resolved? > > There have been interludes, but not much in the way of discussion. > Hopefully, this will be a starting point. > > Thanks, > Dan > > [1] http://marc.info/?l=linux-raid&m=123300614013042&w=2 dm-devel should be cc'd to get a dialog going with the DM team. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
