Thank You. On Wed, May 18, 2016 at 11:54 AM, Sage Weil <sage@xxxxxxxxxxxx> wrote: > On Wed, 18 May 2016, Chandan Kumar Singh wrote: >> I can understand the complexities now. Still, there is a little bit of >> surprise element when large number of xattrs can be stored in leveldb >> but not omaps. Are these xattrs not being erasure coded and >> distributed over nodes? When EC pools are space efficient alternative >> to replicated pools, not having omaps defeats the purpose for anyone >> who uses omaps extensively. I can guess that some users might be >> storing the key-value kind of metadata in some external store. > > That's exactly the issue: xattrs are replicated across all OSDs in the PG > (and also appear in pg log entries). We didn't implement a way to > erasure code key/value data (and it's not obvious how one should do so). > > For now, heavy omap users should just stick to replication. > > sage > > >> >> On Wed, May 18, 2016 at 2:11 AM, Sage Weil <sage@xxxxxxxxxxxx> wrote: >> > On Tue, 17 May 2016, Chandan Kumar Singh wrote: >> >> Thanks. Why are omaps not allowed for objects in EC pools? >> > >> > Because it doesn't make much sense to erasure code small key=value pairs >> > over lots of nodes. Values are too small to be individually encoded >> > sensibly, and packing them together would require a layer of complexity. >> > It could presumably be done, but we didn't do it, and have yet to hear >> > from someone who really needs it. >> > >> > sage >> > >> > >> > >> >> >> >> On Tue, May 17, 2016 at 7:22 PM, Sage Weil <sage@xxxxxxxxxxxx> wrote: >> >> > On Tue, 17 May 2016, Chandan Kumar Singh wrote: >> >> >> Hi >> >> >> >> >> >> While migrating to EC pools, I came to know that it does not support >> >> >> omaps but it allows thousands of xattrs (XFS). Are these xattrs being >> >> >> stored in a key-value store or in XFS file system? >> >> > >> >> > They are stored in XFS, until there are more than a handful, after which >> >> > point they get stored in leveldb. But they are *also* stored in every pg >> >> > log event that modifies the object, so you should definitely not (ab)use >> >> > xattrs the way you would use omap and expect the system to behave/perform! >> >> > They are meant to be small and few. >> >> > >> >> > sage >> >> >> >> >> >> -- 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
