[LUDOC-154] Add wide striping content to Lustre manual (Ch 18)

• Status: Resolved
• Project: Lustre Documentation
• Type: Improvement
• Priority: Major
• Reporter: Brett Lee (Inactive)
• Assignee: Linda Bebernes (Inactive)
• Resolution: Fixed
• Labels: QContent
• Business Value: 6

Description

Cut/paste from Skype discussion with Andreas - 5/18/2013.

Brett Lee: wide striping requires a seperate inode for the EA that holds the ostnum:objectnum's?  does this mean that we cannot simply size a MDT by 2K inodes per file?  thanks.

Andreas Dilger: Brett: up to 160 stripes fit into a single 4kB block. beyond that, we allocate a new "xattr inode" to hold the xattr data. this needs to be enabled either at format time with "mkfs.lustre --mkfsoptions='-O large_xattr' ... /dev/

{mdsdev}" or afterward with "tune2fs -O large_xattr /dev/{mdsdev}

".

for wide striping the inode size isn't relevant, since it needs to be stored externally. now if every file had wide striping, then you would need to create fewer inodes (i.e. higher bytes per inode ratio) or the MDS would run out of space before inodes. that is very unlikely, however, so we don't consider this case by default

Comments

[Linda Bebernes (Inactive)]

Is Chapter 18 - Managing File Striping - where this belongs?

Currently "wide striping" is mentioned in 16.2 (Upgrade chapter) and the Glossary.

[Linda Bebernes (Inactive)]

Brett Lee has provided this text to add to a new section at the end of Chapter 18:
Prior to Lustre 2.2, the maximum stripe count of a single Lustre file was limited to160 objects. This limit was imposed by the structure of a Lustre inode and the spaceavailable in the Extended Attribute that tracked the objects in a Lustre file.
From version 2.2, the limitation of 160 objects has been raised to 2000. This has been accomplished by allowing a data block to be used for the extended attribute that holdsthe object information. This feature, known as wide striping, only allocates the newblock if the object is created with a stripe size greater than 160 - and in that caseall the object information (not just those objects greater than 160) are allocated inthe new block. For files smaller than 160 objects, no additional data block is referenced by the inode

[Linda Bebernes (Inactive)]

Patch ready for review at http://review.whamcloud.com/#/c/7042/

[Linda Bebernes (Inactive)]

Changes approved and merged 7 Aug 2013.