Ceph distributed filesystem merged for 2.6.34
Posted Mar 23, 2010 18:58 UTC (Tue) by martinfick
In reply to: Ceph distributed filesystem merged for 2.6.34
Parent article: Ceph distributed filesystem merged for 2.6.34
"Also, why do people still like implementing POSIX filesystem semantics on distributed filesystems? Intuitively it seems like POSIX semantics demand a really fast interconnect between nodes. In contrast, systems that implement weaker forms of consistency, like the Andrew File System, can perform well with lower-end networking gear. I think most system administrators would be satisfied with something like AFS's open-to-close consistency guarantee. I mean, most system administrators still use NFS, which has horrible consistency semantics.
Why do people implement them? Probably because users want them! I know I do. Afterall, surely you can agree that POSIX semantics are useful? We like them on our local filesystems. Why would I not like them on distributed ones? Granted, they are likely to have high latencies, but that doesn't mean that I don't want POSIX semantics.
Yes, AFS/NFS semantics are fine for some applications, but there are many for which it is not. With today's virtualization trend, it becomes more and more important to be able to use shared/distributed filesystems, but this is of little use if one has to think about which virtualized applications really need POSIX and which do not, and then segregate accordingly.
So, users want POSIX whether local or distributed (try asking ext4/ZFS/BTRFS why they feel the need to implement POSIX.) And, of course, the holy grail for many sysadmins would be a fast/distributed/scalable/HA/POSIX fs which ceph promises to be. I am happy that ceph is at least attempting to do this. You seem to imply that there are tons of FSes doing this, who else is?
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