Le 24/08/2015 19:34, Robert LeBlanc a écrit : > Building off a discussion earlier this month [1], how "supported" is > EXT4 for OSDs? It seems that some people are getting good results with > it and I'll be testing it in our environment. > > The other question is if the EXT4 journal is even necessary if you are > using Ceph SSD journals. My thoughts are thus: Incoming I/O is written > to the SSD journal. The journal then flushes to the EXT4 partition. > Only after the write is completed (I understand that this is a direct > sync write) does Ceph free the SSD journal entry. > > Doesn't this provide the same reliability as the EXT4 journal? If an > OSD crashed in the middle of the write with no EXT4 journal, the file > system would be repaired and then Ceph would rewrite the last > transaction that didn't complete? I'm sure I'm missing something > here... I didn't try this configuration but what you miss is probably : - the file system recovery time when there's no journal available. e2fsck on large filesystems can be long and may need user interaction. You don't want that if you just had a cluster-wide (or even partial but involving tens of disks some of which might be needed to reach min_size) power failure. - the less tested behaviour: I'm not sure there's even a guarantee from ext4 without journal than e2fsck can recover properly after a crash (ie: with data consistent with the Ceph journal). Lionel _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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