2015-07-23 12:35:35 +00:00
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CephFS Quotas
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=============
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CephFS allows quotas to be set on any directory in the system. The
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quota can restrict the number of *bytes* or the number of *files*
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stored beneath that point in the directory hierarchy.
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Limitations
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-----------
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#. *Quotas are cooperative and non-adversarial.* CephFS quotas rely on
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the cooperation of the client who is mounting the file system to
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stop writers when a limit is reached. A modified or adversarial
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client cannot be prevented from writing as much data as it needs.
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Quotas should not be relied on to prevent filling the system in
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environments where the clients are fully untrusted.
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#. *Quotas are imprecise.* Processes that are writing to the file
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system will be stopped a short time after the quota limit is
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reached. They will inevitably be allowed to write some amount of
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data over the configured limit. How far over the quota they are
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able to go depends primarily on the amount of time, not the amount
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of data. Generally speaking writers will be stopped within 10s of
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seconds of crossing the configured limit.
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#. *Quotas are not yet implemented in the kernel client.* Quotas are
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supported by the userspace client (libcephfs, ceph-fuse) but are
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not yet implemented in the Linux kernel client.
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#. *Quotas must be configured carefully when used with path-based
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mount restrictions.* The client needs to have access to the
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directory inode on which quotas are configured in order to enforce
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them. If the client has restricted access to a specific path
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(e.g., ``/home/user``) based on the MDS capability, and a quota is
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2015-12-01 09:15:29 +00:00
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configured on an ancestor directory they do not have access to
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2015-07-23 12:35:35 +00:00
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(e.g., ``/home``), the client will not enforce it. When using
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path-based access restrictions be sure to configure the quota on
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the directory the client is restricted too (e.g., ``/home/user``)
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or something nested beneath it.
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Configuration
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-------------
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Like most other things in CephFS, quotas are configured using virtual
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extended attributes:
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* ``ceph.quota.max_files`` -- file limit
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* ``ceph.quota.max_bytes`` -- byte limit
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If the attributes appear on a directory inode that means a quota is
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configured there. If they are not present then no quota is set on
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that directory (although one may still be configured on a parent directory).
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To set a quota::
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setfattr -n ceph.quota.max_bytes -v 100000000 /some/dir # 100 MB
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setfattr -n ceph.quota.max_files -v 10000 /some/dir # 10,000 files
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To view quota settings::
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getfattr -n ceph.quota.max_bytes /some/dir
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getfattr -n ceph.quota.max_files /some/dir
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Note that if the value of the extended attribute is ``0`` that means
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the quota is not set.
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To remove a quota::
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setfattr -n ceph.quota.max_bytes -v 0 /some/dir
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setfattr -n ceph.quota.max_files -v 0 /some/dir
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