On Fri, Jan 10, 2014 at 11:13 AM, Gregory Farnum <greg@xxxxxxxxxxx> wrote: > Exactly. We can't do a safe update without a journal — what if power > goes out while the write is happening? When we boot back up, we don't > know what version the object is actually at. So if you're using btrfs, > you can run without a journal already (and depend on snapshots for > recovering after failures); if you are using xfs or ext4 a journal is > required for any safety at all, even when it's fronted by a cache > pool. I'm not fully agree with it. Why we can't call "fdatasync()" during each transaction to ensure consistent if exists cache in the front of. > > On Thu, Jan 9, 2014 at 7:08 PM, Dong Yuan <yuandong1222@xxxxxxxxx> wrote: >> The Journal is the part of implementation of ObjectStore Transaction >> Interface, while transaction is used by PG to write pglog with object >> data in one transaction. >> So I think if the FileJournal could be disabled, there must be >> something else to implement the Transaction Interface. But it seems >> hard while no local file-system provide such function in my opinion. >> >> >> On 10 January 2014 10:04, Haomai Wang <haomaiwang@xxxxxxxxx> wrote: >>> On Fri, Jan 10, 2014 at 1:28 AM, Gregory Farnum <greg@xxxxxxxxxxx> wrote: >>>> >>>> The FileJournal is also for data safety whenever we're using write >>>> ahead. To disable it we need a backing store that we know can provide >>>> us consistent checkpoints (i.e., we can use parallel journaling mode — >>>> so for the FileJournal, we're using btrfs, or maybe zfs someday). But >>>> for those systems you can already configure the system not to use a >>>> journal. >>> >>> Yes, it depends on backend. For example, FileStore can write a object with sync >>> to sure consistent. If adding a disable FileJournal option, we need >>> some works on >>> FileStore to implement it. >>> >>>> -Greg >>>> Software Engineer #42 @ http://inktank.com | http://ceph.com >>>> >>>> >>>> On Thu, Jan 9, 2014 at 12:13 AM, Haomai Wang <haomaiwang@xxxxxxxxx> wrote: >>>> > Hi all, >>>> > >>>> > We know FileJournal plays a important role in FileStore backend, it can >>>> > hugely reduce write latency and improve small write operations. >>>> > >>>> > But in practice, there exists exceptions such as we already use FlashCache or cachepool(although it's not ready). >>>> > >>>> > If cachepool enabled, we may use use journal in cache_pool but may >>>> > not like to use journal in base_pool. The main reason why drop journal >>>> > in base_pool is that journal take over a single physical device and waste >>>> > too much in base_pool. >>>> > >>>> > Like above, if I enable FlashCache or other cache, I'd not like to enable >>>> > journal in OSD layer. >>>> > >>>> > So is it necessary to disable journal in special(not really special) case? >>>> > >>>> > Best regards, >>>> > Wheats >>>> > >>>> > >>>> > >>>> > -- >>>> > 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 >>> >>> >>> >>> >>> -- >>> >>> Best Regards, >>> >>> Wheat >>> -- >>> 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 >> >> >> >> -- >> Dong Yuan >> Email:yuandong1222@xxxxxxxxx -- Best Regards, Wheat -- 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
