OK, that's clear. Nice space simulator btw :-) you should add a link somewhere in btrfs wiki...
Thanks ---------------------------------------- > Date: Thu, 26 Sep 2013 14:46:05 +0100 > From: h...@carfax.org.uk > To: miaous...@hotmail.com > CC: linux-btrfs@vger.kernel.org > Subject: Re: [raidX vs single/dup] > > On Thu, Sep 26, 2013 at 01:40:57PM +0000, miaou sami wrote: >> Thank you, it is quite clear now. >> >> >> I guess that on multi device, raid0 vs single would be a matter of >> performance vs ease of low level hardware data recovery. >> >> >> The wiki >> https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices >> says: >> "When you have drives with differing sizes and want to use the full capacity >> of each drive, you have to use the single profile for the data blocks." >> Let's assume the following configuration: 1x10GB disk and 2x5GB disks >> --> Does it mean I cannot use the full capacity AND have a duplication of my >> data in the configuration above? (full capacity would be 10GB here) > > No, that will give you the full usable space. A 20 GB drive and two > 5 GB drives would not, though. > >> --> If I try to setup either -d raid1 or -d dup on that >> configuration, what will I get? > > Try it for yourself in the space simulator: > > http://carfax.org.uk/btrfs-usage/ > >> --> Is there any behavior difference between raid1 / dup in that case? > > If you have multiple disks, I think DUP gets automatically upgraded > to RAID-1 (i.e. the "different copies on different devices" > requirement is enforced). So, no. > >> --> Can raid1 ensure that data are always duplicated on different devices >> AND take advantage of all available space? > > Depends on the relative sizes of the devices. If your largest > device is bigger than the rest put together, then you'll lose some > space. > > Hugo. > >> Regards, >> Sam >> >> >> ---------------------------------------- >>> Date: Thu, 26 Sep 2013 13:32:33 +0100 >>> From: h...@carfax.org.uk >>> To: miaous...@hotmail.com >>> CC: linux-btrfs@vger.kernel.org >>> Subject: Re: [raidX vs single/dup] >>> >>> On Thu, Sep 26, 2013 at 12:22:49PM +0000, miaou sami wrote: >>>> Hi btrfs guys, >>>> >>>> could someone explain to me the differences in mkfs.btrfs: >>>> >>>> - between -d raid0 and -d single >>> >>> In RAID0, data is striped across all the devices, so the first 64k >>> of a file will go on device 1, the next 64k will go on device 2, and >>> so on. With single, files are allocated linearly on one device. >>> >>> (This is assuming smallish files, a filesystem with lots of space. >>> Even with single, files can still end up being scattered around over >>> multiple devices -- but with RAID0, even non-fragmented files are >>> striped) >>> >>>> - between -m raid1 and -m dup >>> >>> In both cases, there are two copies of each metadata block. With >>> RAID1, it *requires* the two copies to live on different devices. With >>> DUP, it allows the two copies to live on the same device (e.g. if >>> there's only one device). >>> >>>> - between -m raid0 and -m single >>> >>> As for -draid0 and -dsingle, but for metadata instead of data. >>> >>>> My understanding is that raidX should be used in case of multi >>>> devices and single/dup should be used in case of single device to >>>> allow duplication, but it is not 100% clear to me... >>> >>>> As btrfs raid concepts are quite different from traditionnal raid, >>>> shouldn't we use the words "stripped" and "mirrored" instead of >>>> raid0/raid1? or even "single" and "duplicated"? >>>> Then there would be no difference between single/raid0 and >>>> duplicated/raid1... >>> >>> But there _are_ differences between them, as explained above. :) >>> >>> I posted a patch a while ago to change the names to something more >>> logical and expressive, but it didn't get merged. >>> >>> Hugo. >>> > > -- > === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === > PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk > --- Nothing right in my left brain. Nothing left in --- > my right brain. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
