On Wed, Aug 15, 2012 at 4:50 PM, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> wrote: > On 8/15/2012 5:10 PM, Andy Lutomirski wrote: >> On Wed, Aug 15, 2012 at 3:00 PM, Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> wrote: >>> On 8/15/2012 12:57 PM, Andy Lutomirski wrote: >>>> On Wed, Aug 15, 2012 at 4:50 AM, John Robinson >>>> <john.robinson@xxxxxxxxxxxxxxxx> wrote: >>>>> On 15/08/2012 01:49, Andy Lutomirski wrote: >>>>>> >>>>>> If I do: >>>>>> # dd if=/dev/zero of=/dev/md0p1 bs=8M >>>>> >>>>> [...] >> >> Grr. I thought the bad old days of filesystem and related defaults >> sucking were over. > > The previous md chunk default of 64KB wasn't horribly bad, though still > maybe a bit high for alot of common workloads. I didn't have eyes/ears > on the discussion and/or testing process that led to the 'new' 512KB > default. Obviously something went horribly wrong here. 512KB isn't a > show stopper as a default for 0/1/10, but is 8-16 times too large for > parity RAID. > >> cryptsetup aligns sanely these days, xfs is >> sensible, etc. > > XFS won't align with the 512KB chunk default of metadata 1.2. The > largest XFS journal stripe unit (su--chunk) is 256KB, and even that > isn't recommended. Thus mkfs.xfs throws an error due to the 512KB > stripe. See the md and xfs archives for more details, specifically Dave > Chinner's colorful comments on the md 512KB default. Heh -- that's why the math didn't make any sense :) > >> wtf? <rant>Why is there no sensible filesystem for >> huge disks? zfs can't cp --reflink and has all kinds of source >> availability and licensing issues, xfs can't dedupe at all, and btrfs >> isn't nearly stable enough.</rant> > > Deduplication isn't a responsibility of a filesystem. TTBOMK there are > two, and only two, COW filesystems in existence: ZFS and BTRFS. And > these are the only two to offer a native dedupe capability. They did it > because they could, with COW, not necessarily because they *should*. > There are dozens of other single node, cluster, and distributed > filesystems in use today and none of them support COW, and thus none > support dedup. So to *expect* a 'sensible' filesystem to include dedupe > is wishful thinking at best. I should clarify my rant for the record. I don't care about in-fs dedupe. I want COW so userspace can dedupe and generally replace hardlinks with sensible cowlinks. I'm also working on some fun tools that *require* reflinks for anything resembling decent performance. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
