[LUDOC-102] Put descriptions of "Inode size" and "Bytes per inode" in context for user (Ch 5)

• Status: Resolved
• Project: Lustre Documentation
• Type: Improvement
• Priority: Minor
• Reporter: Linda Bebernes (Inactive)
• Assignee: Linda Bebernes (Inactive)
• Resolution: Fixed
• Labels: QContent
• Business Value: 4

Description

These definitions were included as help snippets in the Chroma UI. They were derived from definitions in the Lustre manual.

Inode size
Size (in bytes) of the inodes used to store Lustre metadata on the MDS for each file. Default is 512 bytes. In the "Lustre Operations Manual", see Section 5.3.1: Setting the Number of Inodes for the MDS.

Bytes per inode
File system space (in bytes) per MDS inode. Default is 2048 (i.e., one MDS inode per each 2048 bytes of file system space). In the "Lustre Operations Manual", see Section 5.3.3: Setting the Number of Inodes for the MDS.

The following comments were submitted in a Chroma ticket (HYD-951) by Brian Murrell. Addressing these is out of scope for Chroma, so I've created this ticket to capture them for the Lustre manual.
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... first sentence in the help bubble for "Bytes per inode" is

File system space (in bytes) per MDS inode.

Both that sentence and the field name "Bytes per inode" mean to me, how many bytes should be in each inode, but that's what the other option "Inode size" is really referring to. It does become clearer as I read more into the help bubble that it really means create an inode for each $n bytes of space in the file system but I wonder if that clarity is in part because I understand these concepts.

Nowhere in the help text for either is there any explanation of why I would want to change these sizes or what the results are of changing them either in terms of how many files I can have in my file system or how many stripes I have without allocating another block and what other impacts there are to using values that reduce the free space available on the MDT. These are the things people really care about...

I think this needs to be approached entirely differently and put into terms that people creating file systems will actually care about which is

■how many files can my file system have
■how many stripes can my files have before incurring performance penalties
■what other penalties I might incur given the values I have provided

Issue Links

• is related to: LUDOC-49 MDT calculations don't include stripi...

Comments

[Linda Bebernes (Inactive)]

Reworked section 5.3 "Setting File System Formatting Options" to correct errors and make it more clear.

Brian's comments about creating file systems are not completely addressed by this change. A new ticket LUDOC-163 has been opened to address his concerns in Chapter 18.

[Linda Bebernes (Inactive)]

Changes are ready for review at http://review.whamcloud.com/#/c/6847/

[Linda Bebernes (Inactive)]

Changes merged.