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 -- 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
