August 2019 - Dev - lists.ceph.io

by Sage Weil

Hi Myoungwon, I was thinking about how a refcounted cas pool would interact with snapshots and it occurred to me that dropping refs when an object is deleted may break snapshotted versions of that object. If object A has a ref to chunk X, is snapshotted, then A is deleted, we'll (currently) drop the ref to X and remove it. That means that A can't be read. One way to get around that would be to mirror snaps from the source pool to the chunk pool--this is how cache tiering works. The problem I see there is that I'd hoped to allow multiple pools to share/consume the same chunk pool, but each pool has its own snapid namespace. Another would be to bake the refs more deepling into the source rados pool so that the refs are only dropped after all clones also drop the ref. That is harder to track, though, since I think you'd need to examine all of the clones to know whether the ref is truly gone. Unless we embed even more metadata in the SnapSet--something analogous to clone_overlap to identifying the chunks. That seems like it will bloat that structure, though. Other ideas? sage

4 years, 8 months

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Integrating Ceph with the Kubernetes Events API

by Paul Cuzner

Hi, I've been working on a mgr module to push some types of ceph system activity into the kubernetes events api, so kubernetes users get a more granular view of what's going on within the ceph cluster. The code is not complete, but if you're interested it's here - https://github.com/pcuzner/ceph/blob/add-events-mgr-module/src/pybind/mgr/k… At this point it does the following; - ties into the log_monitor2 rados call to pick up audit and healthcheck messages - creates an hourly health heartbeat (health + capacity) - emits events for configuration changes - host add/remove - osd add/remove - pool add/remove - pool size and min_size changes Interested to hear if there are any other ceph 'events' that I should be considering Cheers, PC

4 years, 8 months

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protecting snapshots

by Jan Fajerski

Hi list, while discussing the snap-schedule module, a feature request for protecting snapshots against deletion came up. This is partly tied to the scheduled pruning, when a user wants to protect an individual snapshot from being pruned. It could however also be used to protect individual snapshots from being accidentally deleted. One proposed interface (thx Lars) would be to implement a new extended attribute on snapshot directories. I like this as an interface as its quiet flexible and could be build upon (by say a mgr module command). Does snapshot deletion involve the MDS? Otherwise older clients not aware might still delete them (like quotas depend on client cooperation) Is a virtual xattr on a virtual directory a bad idea? Other concerns or better ideas? Best, Jan

4 years, 8 months

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Static Analysis, including Coverity results

by Brad Hubbard

Latest static analyser results are up on http://people.redhat.com/bhubbard/ This week's run includes Coverity results. I'll be sending a separate email about the status of Coverity results in the next couple of days. Weekly Fedora Copr builds are at https://copr.fedorainfracloud.org/coprs/badone/ceph-weeklies/ -- Cheers, Brad

4 years, 8 months

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4 years, 8 months

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libcephfs and supplimentary groups

by David Disseldorp

Hi, Without calling ceph_mount_perms_set(), libcephfs consumers such as Samba can rely upon UserPerm::uid() and UserPerm::gid() to fallback to geteuid() and setegid() respectively for things such as ACL enforcement. However, there is no such fallback for supplementary groups, so ACL checks for a user which is only permitted path access via a supplementary group will result in a permission denied error. Samba ticket: https://bugzilla.samba.org/show_bug.cgi?id=14053 I've written a patch to address this (it currently omits the get_gids() codepath): https://github.com/ddiss/ceph/commit/035a1785ec73d803fead42c7240df01b755a81… Does this approach make sense, or should Samba go down the ceph_mount_perms_set() route to avoid this bug? The latter would likely be problematic, as user/group details for a mount will remain static. Cheers, David

4 years, 8 months

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Adventures with large RGW buckets

by Paul Emmerich

Hi, we are seeing a trend towards rather large RGW S3 buckets lately. we've worked on several clusters with 100 - 500 million objects in a single bucket, and we've been asked about the possibilities of buckets with several billion objects more than once. From our experience: buckets with tens of million objects work just fine with no big problems usually. Buckets with hundreds of million objects require some attention. Buckets with billions of objects? "How about indexless buckets?" - "No, we need to list them". A few stories and some questions: 1. The recommended number of objects per shard is 100k. Why? How was this default configuration derived? It doesn't really match my experiences. We know a few clusters running with larger shards because resharding isn't possible for various reasons at the moment. They sometimes work better than buckets with lots of shards. So we've been considering to at least double that 100k target shard size for large buckets, that would make the following point far less annoying. 2. Many shards + ordered object listing = lots of IO Unfortunately telling people to not use ordered listings when they don't really need them doesn't really work as their software usually just doesn't support that :( A listing request for X objects will retrieve up to X objects from each shard for ordering them. That will lead to quite a lot of traffic between the OSDs and the radosgw instances, even for relatively innocent simple queries as X defaults to 1000 usually. Simple example: just getting the first page of a bucket listing with 4096 shards fetches around 1 GB of data from the OSD to return ~300kb or so to the S3 client. I've got two clusters here that are only used for some relatively low-bandwidth backup use case here. However, there are a few buckets with hundreds of millions of objects that are sometimes being listed by the backup system. The result is that this cluster has an average read IO of 1-2 GB/s, all going to the index pool. Not a big deal since that's coming from SSDs and goes over 80 Gbit/s LACP bonds. But it does pose the question about scalability as the user- visible load created by the S3 clients is quite low. 3. Deleting large buckets Someone accidentaly put 450 million small objects into a bucket and only noticed when the cluster ran full. The bucket isn't needed, so just delete it and case closed? Deleting is unfortunately far slower than adding objects, also radosgw-admin leaks memory during deletion: https://tracker.ceph.com/issues/40700 Increasing --max-concurrent-ios helps with deletion speed (option does effect deletion concurrency, documentation says it's only for other specific commands). Since the deletion is going faster than new data is being added to that cluster the "solution" was to run the deletion command in a memory-limited cgroup and restart it automatically after it gets killed due to leaking. How could the bucket deletion of the future look like? Would it be possible to put all objects in buckets into RADOS namespaces and implement some kind of efficient namespace deletion on the OSD level similar to how pool deletions are handled at a lower level? 4. Common prefixes could filtered in the rgw class on the OSD instead of in radosgw Consider a bucket with 100 folders with 1000 objects in each and only one shard /p1/1, /p1/2, ..., /p1/1000, /p2/1, /p2/2, ..., /p2/1000, ... /p100/1000 Now a user wants to list / with aggregating common prefixes on the delimiter / and wants up to 1000 results. So there'll be 100 results returned to the client: the common prefixes p1 to p100. How much data will be transfered between the OSDs and radosgw for this request? How many omap entries does the OSD scan? radosgw will ask the (single) index object to list the first 1000 objects. It'll return 1000 objects in a quite unhelpful way: /p1/1, /p1/2, ...., /p1/1000 radosgw will discard 999 of these and detect one common prefix and continue the iteration at /p1/\xFF to skip the remaining entries in /p1/ if there are any. The OSD will then return everything in /p2/ in that next request and so on. So it'll internally list every single object in that bucket. That will be a problem for large buckets and having lots of shards doesn't help either. This shouldn't be too hard to fix: add an option "aggregate prefixes" to the RGW class method and duplicate the fast-forward logic from radosgw in cls_rgw. It doesn't even need to change the response type or anything, it just needs to limit entries in common prefixes to one result. Is this a good idea or am I missing something? IO would be reduced by a factor of 100 for that particular pathological case. I've unfortunately seen a real-world setup that I think hits a case like that. Paul -- Paul Emmerich Looking for help with your Ceph cluster? Contact us at https://croit.io croit GmbH Freseniusstr. 31h 81247 München www.croit.io Tel: +49 89 1896585 90

4 years, 8 months

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Re: [ceph-users] details about cloning objects using librados

by Brad Hubbard

On Thu, Jun 27, 2019 at 8:58 PM nokia ceph <nokiacephusers(a)gmail.com> wrote: > > Hi Team, > > We have a requirement to create multiple copies of an object and currently we are handling it in client side to write as separate objects and this causes huge network traffic between client and cluster. > Is there possibility of cloning an object to multiple copies using librados api? > Please share the document details if it is feasible. It may be possible to use an object class to accomplish what you want to achieve but the more we understand what you are trying to do, the better the advice we can offer (at the moment your description sounds like replication which is already part of RADOS as you know). More on object classes from Cephalocon Barcelona in May this year: https://www.youtube.com/watch?v=EVrP9MXiiuU > > Thanks, > Muthu > _______________________________________________ > ceph-users mailing list > ceph-users(a)lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com -- Cheers, Brad

4 years, 8 months

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07/25/2019 perf meeting is on!

by Mark Nelson

Hi Folks, Perf meeting is on in ~15 minutes! Today let's talk about bluestore min_alloc_size, bluefs_alloc_size, and the trade-offs of combining these into one option. Please feel free to add your own topic as well! Etherpad: https://pad.ceph.com/p/performance_weekly Bluejeans: https://bluejeans.com/908675367 Thanks, Mark

4 years, 8 months

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Dev August 2019