KenRawlings: assigning category

2016-03-04T18:47:15Z

assigning category

← Older revision		Revision as of 11:47, 4 March 2016
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	http://www.opensolaris.org/jive/thread.jspa?threadID=39817&tstart=15		http://www.opensolaris.org/jive/thread.jspa?threadID=39817&tstart=15

			[[Category: Architecture]]

Adilger: /* References */ add link to GitHub tracker

2015-09-14T23:25:15Z

References: add link to GitHub tracker

← Older revision		Revision as of 16:25, 14 September 2015
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	== References ==		== References ==
			[https://github.com/zfsonlinux/zfs/pull/3542\|Large dnode pool feature]

	http://www.opensolaris.org/jive/thread.jspa?threadID=39817&tstart=15		http://www.opensolaris.org/jive/thread.jspa?threadID=39817&tstart=15

Adilger: Copy from original page on old wiki

2015-09-14T23:04:21Z

Copy from original page on old wiki

New page

'''''Note:''''' ''The content on this page reflects the state of design of a Lustre feature at a particular point in time and may contain outdated information.''

== Definitions ==

; '''dnode''' : DMU node, 512 bytes in original ZFS implementation and includes "bonus buffer" for users to store extra data
; '''EA''' : extended attribute generally of a limited size (4kB or less), not to be confused with the ZFS 'xattr' which is more like a named byte stream that may be an arbitrary size
; '''znode''' : ZPL-format dnode, uses bonus buffer to store POSIX data for ZFS
== Use Cases ==

{| border=1 cellspacing=0
|-
!id !! quality attribute !! summary
|-
|large_dnode || performance || increased dnode size to allow more data in the inode
|}

=== EA in large dnode ===

{|border=1 cellspacing="0"
|-align="left"
|colspan=2|'''Scenario:''' || Storage of EA in dnode
|-align="left"
|colspan=2|'''Business Goals:''' || Fast access to Lustre EA values
|-align="left"
|colspan=2|'''Relevant QA's:'''|| Performance
|-align="left"
|rowspan="6" writing-mode="vertical"|'''details'''
| '''Stimulus:'''|| EA needs to be stored in ZFS-format dnode
|-align="left"
|'''Stimulus source:'''|| Lustre OSD (MDT/OST) storing EA data to object
|-align="left"
|'''Environment:'''|| EA being stored on a specific znode within a transaction
|-align="left"
|'''Artifact:'''|| EA is stored in the znode
|-align="left"
|'''Response:'''|| time to store EA data
|-align="left"
|'''Response measure:'''|| time is not significantly more than znode update without EA, much less than storing data in ZFS xattr
|-align="left"
|colspan=2|'''Questions:'''||
|-align="left"
|colspan=2|'''Issues:'''|| None.
|-
|}

== Implementation constraints ==

DMU must work with both larger and original size dnodes in the same pool. There is currently no requirement for dynamic dnode size within a single filesystem

ZFS must be able to work on a filesystem with large dnodes, even if it cannot initially access the extra dnode space

'zfs' tool must be able to specify dnode size for a filesystem at creation time

EA is stored in microzap (as described in [[Architecture - ZFS_TinyZAP|ZFS_Microzap]]) to allow efficient access, retrieval, and flexibility.

== Questions and Issues ==

How do we handle case where EAs overflow available space in dnode? Strong consideration should be given to allowing EAs (also?) be stored in an external block or in a protected EA xattr file.

== References ==

http://www.opensolaris.org/jive/thread.jspa?threadID=39817&tstart=15

Architecture - ZFS large dnodes - Revision history

KenRawlings: assigning category

Adilger: /* References */ add link to GitHub tracker

Adilger: Copy from original page on old wiki