On 01/14/2013 06:34 PM, Gregory Farnum wrote: > On Mon, Jan 14, 2013 at 6:09 AM, Florian Haas <florian@xxxxxxxxxxx> wrote: >> Hi Mark, >> >> thanks for the comments. >> >> On Mon, Jan 14, 2013 at 2:46 PM, Mark Nelson <mark.nelson@xxxxxxxxxxx> wrote: >>> Hi Florian, >>> >>> Couple of comments: >>> >>> "OSDs use a write-ahead mode for local operations: a write hits the journal >>> first, and from there is then being copied into the backing filestore." >>> >>> It's probably important to mention that this is true by default only for >>> non-btrfs file systems. See: >>> >>> http://ceph.com/wiki/OSD_journal >> >> I am well aware of that, but I've yet to find a customer (or user) >> that's actually willing to entrust a production cluster with several >> hundred terabytes of data to btrfs. :) Besides, the whole post is >> about whether or not to use dedicated SSD block devices for OSD >> journals, and if you're tossing everything into btrfs you've already >> made the decision to use in-filestore journals. > > That is absolutely not the case. btrfs works just fine with an > external journal on SSD or whatever else; what made you think > otherwise? A misunderstanding on my part. Also, I was overly broad in my comment. What I really meant to say was that if I'm using a btrfs filestore, and a separate dedicated block device for the journal, then the journaling mode is write-ahead and not parallel. Which was a wrong assumption on my part, as an external journal combined with a btrfs filestore seems to support parallel journaling mode just fine. For some reason I had supposed the journal had to be in the same btrfs as the filestore for this to work. Sorry for the confusion. Cheers, Florian -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
