I'm wondering how the write-behind xlator is supposed to work when accessing files O_SYNC. Looking at https://github.com/gluster/glusterfs/blob/v3.3.1/xlators/performance/write-behind/src/write-behind.c#L1386, one might get the impression that all access using O_SYNC should have write-behind disabled ? Using loop devices backed by files on Gluster, I'm usually able to do O_SYNC writes at ~25MB/s. After ~24 hours at that transfer rate, the rate drops to ~3MB/s. This performance degradation is accompanied by the following lines in the client log: torbjorn at xen-storage01:~$ grep 'disabling wb' glusterfs.log [2013-03-08 01:11:43.452718] D [write-behind.c:1392:wb_open_cbk] 4-gluster0-write-behind: disabling wb on 0x7f71249023cc [2013-03-08 01:11:43.470332] D [write-behind.c:1349:wb_disable_all] 4-gluster0-write-behind: disabling wb on 0x7f7139c23abc because 0x7f71249023cc is O_SYNC [2013-03-08 01:24:22.052691] D [write-behind.c:1392:wb_open_cbk] 4-gluster0-write-behind: disabling wb on 0x7f71249023cc [2013-03-08 01:26:22.114299] D [write-behind.c:1392:wb_open_cbk] 4-gluster0-write-behind: disabling wb on 0x7f71249023cc [2013-03-08 01:26:52.179240] D [write-behind.c:1392:wb_open_cbk] 4-gluster0-write-behind: disabling wb on 0x7f71249023cc [2013-03-08 01:27:13.735775] D [write-behind.c:1392:wb_open_cbk] 4-gluster0-write-behind: disabling wb on 0x7f71249023cc [2013-03-08 01:27:13.735796] D [write-behind.c:1349:wb_disable_all] 4-gluster0-write-behind: disabling wb on 0x7f7139c23b20 because 0x7f71249023cc is O_SYNC [2013-03-08 01:27:44.261945] D [write-behind.c:1392:wb_open_cbk] 4-gluster0-write-behind: disabling wb on 0x7f71249023cc [2013-03-08 01:28:18.836625] D [write-behind.c:1392:wb_open_cbk] 4-gluster0-write-behind: disabling wb on 0x7f71249023cc [2013-03-08 01:29:09.427915] D [write-behind.c:1392:wb_open_cbk] 4-gluster0-write-behind: disabling wb on 0x7f71249023cc Each of those lines are preceded by a mention of the filename that is being affected: [2013-03-08 01:11:43.428095] D [afr-common.c:1294:afr_lookup_select_read_child] 4-gluster0-replicate-0: Source selected as 0 for /hennec.vps.trollweb.net/disk0 [2013-03-08 01:11:43.428110] D [afr-common.c:1097:afr_lookup_build_response_params] 4-gluster0-replicate-0: Building lookup response from 0 In addition, for a few files I also get these: [2013-03-08 01:11:43.470332] D [write-behind.c:1349:wb_disable_all] 4-gluster0-write-behind: disabling wb on 0x7f7139c23abc because 0x7f71249023cc is O_SYNC Should write-behind be active at all while access is O_SYNC ? It seems that this part of the code has seen major changes between 3.3.1 and 3.4.0, so I will try out the latest alpha and see if I still see the same behavior from write-behind. -- Vennlig hilsen Torbj?rn Thorsen Utvikler / driftstekniker Trollweb Solutions AS - Professional Magento Partner www.trollweb.no Telefon dagtid: +47 51215300 Telefon kveld/helg: For kunder med Serviceavtale Bes?ksadresse: Luramyrveien 40, 4313 Sandnes Postadresse: Maurholen 57, 4316 Sandnes Husk at alle v?re standard-vilk?r alltid er gjeldende