[Docs] [txt|pdf] [Tracker] [WG] [Email] [Nits]

Versions: 00 01 02 03 04 05 06 07 RFC 4331

                                                           L. Dusseault
                                                                 Xythos
   Internet Draft                                             C. Warner
   Document: draft-ietf-webdav-quota-00.txt                     Netezza
   Expires: April 2003                                     October 2002


               Quota and Size Properties for DAV Collections


Status of this Memo
   This document is an Internet-Draft and is in full conformance
   with all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.
   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time.  It is inappropriate to use Internet-Drafts as
   reference material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
        http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
        http://www.ietf.org/shadow.html.

Abstract

   WebDAV servers are frequently deployed with collection quota (size)
   limitations.  This Internet-Draft discusses the two properties and
   minor behaviors needed for clients to interoperate with quota
   implementations on WebDAV repositories.

Table of Contents
   Status of this Memo................................................1
   Abstract...........................................................1
   Introduction.......................................................2
   Requirement for quotas.............................................2
   Solution Overview..................................................2
   Error reporting....................................................5
   Notes..............................................................5
   Security Considerations............................................6
   Internationalization Considerations................................6
   IANA Considerations................................................6
   Intellectual Property..............................................7
   References.........................................................8
   Author's Addresses.................................................8



   Dusseault              Expires April 2003                         1

                    DAV Collection Size and Quota      October 2002



Introduction

   Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in
   this document are to be interpreted as described in RFC 2119
   [RFC2119].


   Requirement for quotas

   WebDAV servers based on [RFC2518] are being implemented and deployed
   with quota restrictions on collections, so it make sense to
   standardize this functionality to improve user experience and client
   interoperability.  This specification requires WebDAV because it
   requires PROPFIND support and relies on the WebDAV definition of
   collections and properties, including the definitions for live and
   protected properties.

   The reasons why WebDAV servers frequently have collection quotas
   enforced are the same reasons why any storage system comes with
   quotas.

    - Sometimes the storage service charges according to quota
   (XDrive.com and www.storeitonline.com have both operated under this
   model)

    - Sometimes the storage service is provided free, but the storage
   service provider has limited storage space (www.sharemation.com has
   this limitation and university-provided student accounts often do as
   well)

    - Even in cases where the storage can be upgraded, the storage
   managers may choose to impose quotas in order to encourage users to
   limit the files they store on the system and to clean up obsolete
   files.  IT departments within corporations may put quotas on
   storage used by employees.

   In order to work best with repositories that support quotas, client
   software should be able to determine and display the quota (limit)
   on any collection.  Further, client software should have some way of
   fairly reliably determining how much storage space is already
   counted towards the quota.

   Solution Overview

   The approach to meeting the requirements and scenarios outlined
   above is simply to define two live properties.  This specification
   can be met on a server by implementing either or both of the
   following two properties.  Both are recommended.


   Dusseault               Expires April 2002                        2

                    DAV Collection Size and Quota       October 2002


   Neither property need be returned in a <DAV:allprop> request though
   the server may include either.  However, these property names MUST
   be returned in a <DAV:propname> request for a resource that supports
   the properties.

DAV:quota-bytes

   Name: quota-bytes
   Namespace: DAV:
   Purpose: Contains the amount of storage space allocated to a
   collection, measured in bytes.
   DTD: <!ELEMENT quota-bytes (#PCDATA) >

   The DAV:quota-bytes property value is the total amount of storage
   space allocated to a collection and all its descendants.  The value
   of this property will usually be protected, although a user with
   sufficient privileges may be permitted to change the value. The
   property is useful even if it is protected. A 403 Forbidden response
   is recommended for attempts to write a protected property.

   A value of 0 indicates that storage is limited to 0.  Users will
   probably not be able to add resources to the collection.

   If a collection has no quota enforced, it should not return this
   property at all.  A client cannot entirely assume that there is no
   quota enforced on a collection that does not have this property, but
   might as well act as if there is no quota.

   If the quota on a collection is reduced, the server MUST NOT delete
   excess files except as selected by an administrator.  Thus, a
   collection may have more storage used than its quota allows.

   Quota is not additive.  A collection only has the quota assigned to
   it, not (in addition) the quota assigned to sub collections or any
   other collections.  Sub-collections can have different quota values
   than parent collections.  These ôsub-quotaös may act as additional
   constraints, or they may be under-constrained and have no effect.
   This can allow the delegation of quota administration from root
   administrators to collection owners.

   Thus, if a collection A contains collection B, and both have quotas
   of 1,000,000 bytes, then collection A can contain up to 1,000,000
   bytes including the bytes used by resources in B.  Collection B,
   then, can only truly contain 1,000,000 bytes of used storage if A is
   empty; it is likely under-constrained.

   This property is OPTIONAL on collections and SHOULD NOT exist on
   non-collection resources.  When a new collection is created, it is
   up to the server to initialize the value appropriately if it chooses
   to.

DAV:quota-used-bytes


   Dusseault               Expires April 2002                        3

                    DAV Collection Size and Quota        October 2002


   Name: quota-used-bytes
   Namespace: DAV:
   Purpose: Contains the amount of storage space used (possibly counted
   towards quota) by a collection, measured in bytes.
   DTD: <!ELEMENT quota-used-bytes (#PCDATA) >

   The DAV:quota-used-bytes value is calculated by the server to
   indicate approximately how much storage space is already taken up by
   this collection and all its descendants (in bytes).  It MUST include
   child collections and all resources inside those child collections.
   It SHOULD include metadata storage size if metadata storage is
   counted against quota limitations.  Support for this property is
   OPTIONAL on collections and SHOULD NOT exist on non-collection
   resources.  A server SHOULD implement this property to the best of
   its ability if it implements the DAV:quota-bytes property.

   The value SHOULD be an accurate account of how the server counts
   what is stored against quota.  Servers MUST NOT implement this
   property unless the value is at least as accurate as the client
   could calculate itself by summing values for ôgetcontentlengthö.

   Support for this property enhances the client experience, because
   together with DAV:quota-bytes, the client can manage its files to
   avoid running out of allocated storage space.  Clients may not be
   able to calculate the value adequately on their own, depending on
   how total space used is calculated by the server.

   Note that it is entirely possible for a server to support DAV:quota-
   used-bytes without supporting DAV:quota-bytes or any kind of quota
   system, in which case the value should represent the amount of space
   used in the collection and its descendants.

   Example PROPFIND request and response

   Request:

     PROPFIND /~milele/public/ HTTP/1.1
     Depth: 0
     Host: www.sharemation.com
     Content-Type: text/xml
     Content-Length: 200

     <?xml version="1.0" ?>
     <D:propfind xmlns:D="DAV:">
     <D:prop><D:quota-bytes><D:quota-used-bytes></D:prop>
     </D:propfind>

   Response:

     HTTP/1.1 207 Multi-Status
     Date: Tue, 16 Oct 2001 22:13:39 GMT
     Content-Length: xxx
     Content-Type: text/xml; charset=UTF-8

   Dusseault               Expires April 2002                        4

                    DAV Collection Size and Quota        October2002



     <?xml version="1.0" encoding="utf-8" ?>
     <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>http://www.sharemation.com/~milele/public/</D:href>
       <D:propstat>
         <D:prop>
           <D:quota-bytes>1000000</D:quota-bytes>
           <D:quota-used-bytes>4403350</quota-used-bytes>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     </D:multistatus>

Error reporting

   WebDAV (RFC2518) defines the status code 507 (Insufficient Storage).
   This status code SHOULD be used when a client request (e.g. a PUT,
   PROPFIND, MKCOL, MOVE or COPY) is forbidden because it would exceed
   their allotted quota.  In order to differentiate the response from
   other storage problems, the server SHOULD include an XML error body
   as defined by DeltaV [RFC??] with the <DAV:storage-quota-reached/>
   precondition tag.

   Example error response:

   HTTP/1.1 507 Insufficient Storage
   Content-Length: 100
   Content-Type: text/xml
   <?xml version=ö1.0ö>
   <error xmlns=öDAV:ö>
     <storage-quota-reached/>
   </error>

Notes

   Server implementations store and account for their data in many
   different ways.  Some of the challenges:

    - Some server implementations find it prohibitive to count storage
   used for metadata, others may choose to do so for better accounting.

    - Older versions of resources may be stored as well.

    - Variants of one resource may exist with different content lengths

    - Content may be dynamically generated.

    - Resource bodies can be compressed

    - Some resources may be stored for ôfreeö, not counting against
   quota.

   Dusseault               Expires April 2002                        5

                    DAV Collection Size and Quota        October 2002



   Since server storage accounting can vary so much, clients should
   expect the following:

    - The size of a file on the clientÆs file system, or in a PUT
   message, may not correspond to the amount of storage required by the
   server to store the resource. Thus, the client cannot predict with
   100% accuracy whether a given file will be allowed given the storage
   quota.

    - Deleting a resource may not free up the same amount of storage as
   indicated by the DAV:getcontentlength property defined in [RFC2518]
   for the resource.  If deleting a resource does not free up any
   space, the file has probably been moved to a ôtrashö folder or
   ôrecycle binö.

    - The total size of a collection, DAV:quota-used-bytes, is not
   necessarily a sum of the DAV:getcontentlength properties for
   resources stored in the collection.

    - A quota on a collection may be larger than the quota on a
   collection that contains it.  For example, the quota on /~milele/
   may be 100 MB, but the quota on /~milele/public/ may be unlimited.
   This allows the space used by /~milele/public/ to be as large as the
   quota on /~milele/ allows (depending on the other contents of
   /~milele/) even if the quota on /~milele/ is changed.  Thus, even
   when the quota on a parent collection is changed, it is not
   necessarily required to change the quota on every child or
   descendant collection.

Security Considerations

   A hacker may prefer to store files on collections with a large
   quota.  This isn't strictly a security concern because it doesn't
   make it any easier to store files.  On the other hand, the
   DAV:quota-used-bytes property may make it easier to detect tampering
   or misuse.

   If a server chooses to make the DAV:quota-bytes writable by clients
   with sufficient authorization, then it is opening up a certain
   amount of near-administration functionality to clients.  However, it
   is not required for the DAV:quota-bytes property to be writeable by
   any clients, so a server can easily avoid this consideration.

Internationalization Considerations

   Quota is counted in Arabic numerals expressed in strings. There are
   no internationalization considerations.

IANA Considerations

   There are no IANA considerations.


   Dusseault               Expires April 2002                        6

                    DAV Collection Size and Quota        October 2002



Intellectual Property

   The following notice is copied from [RFC2026], and describes the
   position of the IETF concerning intellectual property claims made
   against this document.

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication and any assurances
   of licenses to be made available, or the result of an attempt made
   to obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification
   can be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard. Please address the information to the IETF Executive
   Director.

Acknowledgements

   Jim Whitehead and Jim Luther provided valuable comments on this
   document.























   Dusseault               Expires April 2002                        7

                    DAV Collection Size and Quota        October 2002


References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
      Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2026] Bradner, S., ôThe Internet Standards Process û Revision
      3ö, BCP 9, RFC2026, October 1996.

   [RFC2518] Goland, Y., Whitehead, E., Faizi, A., Carter, S., and
      Jensen, D., "HTTP Extensions for Distributed Authoring --
      WebDAV", RFC2518, February 1999.

   [RFC3253] Clemm, Geoff, Jim Amsden, Tim Ellison, Chris Kaler, Jim
      Whitehead, "Versioning Extensions to WebDAV", RFC3253, October
      2001.



Author's Addresses
   Lisa Dusseault
   Xythos Software, Inc.
   77 Maiden Lane, Suite 200    Phone:  1-415-248-9004
   San Francisco, CA, USA       Email:  lisa@xythos.com

   Clark Warner
   Netezza Corporation
   200 Crossing Blvd,           Phone: 1-508-665-6800 x889
   Framingham, MA 01702         Email: webdav@thewarners.com


























   Dusseault               Expires Jul 2002                          8


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/