WAFL Internals

Appendix A

Data ONTAP 7-Mode Administration

© 2011 NetApp, Inc. All rights reserved.

Module Objectives

By the end of this module, you should be able to:Describe how data is structure within a WAFL®

(Write Anywhere File Layout) file system on a traditional volume

Explain how data is structure within a WAFL file system in a flexible volume on a 32-bit aggregate

Describe how data is structure within a WAFL file system in a flexible volume on a 64-bit aggregate

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WAFL Structure

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WAFL File System

Is the file system in the Data ONTAP® operating system

Stores metadata in files and uses a buffer tree structure

Allows the Data ONTAP operating system to write metadata files and blocks anywhere on disk (Write Anywhere File Layout)

Is more flexible than traditional file systems, because metadata is not in fixed locations on disk, with the exception of the root inode

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WAFL Block Structure

The WAFL file system organizes data into blocks. Use the vol status -b command to verify block

size.system> vol status -bVolume Block Size (bytes) Vol Size (blocks) FS Size (blocks)------ ------------------ ----------------- ---------------- vol0 4096 7058256 7058256

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WAFL Structure

The WAFL file system is structured into volumes:

Aggregate

vol1

vol1

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WAFL File System and Inodes

WAFL organizes some metadata into inodes.An inode:

– Is a collection of information about a file or directory

– Holds information including: Time and date stampSizeUNIX® permissionsWindows® access control list (ACL)

– Has 192 bytes of data– Is placed in an inode file (inofile)

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vol1

WAFL Structure: Volinfo and Fsinfo Blocks

Every volume has a root inode, which is the starting point of the inode “tree.”

Aggregate

vol1

Root inode

volinfoblock 1

volinfo block 2

fsinfo block 255

fsinfo block

0. . .

Active file system

Snapshot®definitions

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vol1

Inode information is held in the inode file (inofile), a hidden system file.

WAFL Structure: Inofile

Aggregate

vol1

Root inode

Inode file

192-byte inode

Blocks of 4096-byte each

0 21. . . 20

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vol1

For files that are less than 65 bytes, the data is stored within the inode file.

Level 0

Aggregate

vol1

Root inode

Inode file

Small file data inside the

192-byte inode

Small file inode

0 . . . 20

4-KB block

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vol1

For files that are greater than 64 bytes, but less than or equal to 64 KB, a level-1 inode structure is used.

Level 1 In Traditional Volumes

vol1

Root inode

Inode file

32-bit pointersFile inode

. . .0 1 15 4 bytes

DirectData Block

DirectData Block

DirectData Block

4-KB block

0 . . . 20

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Traditional Volume

Traditional Volume Data Structure

Disk

Physical Block

Number (PBN)

500 block number

Volume Block

Number(VBN)

500 block number

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vol1

For files that are greater than 64 bytes but less than or equal to 32 KB, a level-1 inode structure is used.

Level 1 In 32-Bit Aggregates

32-Bit Aggregate

vol1

Root inode

Inode file

. . .0 2 x 4 bytes*

DirectData Block

DirectData Block

DirectData Block

0 . . . 20

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*NOTE: 2 x 4 bytes, because the physical and virtual VBNs are separate

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32-bit pointersFile inode

4-KB block

© 2011 NetApp, Inc. All rights reserved.

Aggregate

Flexible Volume Data Structure

Disk

PvBN456 block

number

vVBN500 block

number

vol1 vol2Disk

vVBN500 block

number

PvBN123 block

number

Physical Virtual Block Number (PvBN) Virtual Volume Block Number (vVBN)

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vol1

For files that are greater than 64 bytes but less than or equal to 16 KB, a level-1 inode structure is used.

Level 1 In 64-Bit Aggregates

64-Bit Aggregate

vol1

Root inode

Inode file

. . .0 2 x 8 bytes

DirectData Block

DirectData Block

4-KB block

0 . . . 20

3

15

64-bit pointersFile inode

© 2011 NetApp, Inc. All rights reserved.

vol1

For files that are greater than 64 KB, but less than or equal to 64 MB, a level-2 inode structure is used.

Level 2 in Traditional Volumes

Root inode

Inode file

. . .

DirectData Block

DirectData Block

DirectData Block

. . . 10230 . . . 10230

0 1 15

0 . . . 20

vol1

16

32-bit pointersFile inode

Up to 16 indirect blocks

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vol1

For files that are greater than 32 KB but less than or equal to 16 MB, a level-2 inode structure is used.

Level 2 in 32-Bit Aggregates

32-Bit Aggregate

vol1

Root inode

Inode file

. . .0

0 . . . 20

1 7

DirectData Block

DirectData Block

DirectData Block

Up to 8 indirect blocks

. . . 5110 . . . 5110

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32-bit pointersFile inode

© 2011 NetApp, Inc. All rights reserved.

vol1

For files that are greater than 16 KB, but less than or equal to 4 MB, a level-2 inode structure is used.

Level 2 In 64-Bit Aggregates

64-Bit Aggregate

vol1

Root inode

Inode file

. . .0

0 . . . 20

3

DirectData Block

DirectData Block

DirectData Block

. . . 2550 . . . 2550

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64-bit pointersFile inode

Up to 4 indirect blocks

© 2011 NetApp, Inc. All rights reserved.

vol1

Each directory inode points to at least one 4-KB block that holds the metadata for the block.

Directories

Aggregate

vol1

Root inode

Inode file

Directory inode

4-KB block Chunks

An array of entries containing 128 rows of 12 bytes

An array of 160 sixteen-byte name chunks

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Entries

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Module Summary

Now that you have completed this module, you should be able to:Describe how data is structure within a WAFL

file system on a traditional volumeExplain how data is structure within a WAFL

file system in a flexible volume on a 32-bit aggregate

Describe how data is structure within a WAFL file system in a flexible volume on a 64-bit aggregate

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