[gpfsug-discuss] Inode size, and system pool subblock

[Olaf Weiser]

ok.. let me give some more context..

all inodes are in a (single) inode file..
so ... depending on the blocksize .. lets say ... 1MB ... you can have 256 inodes (in case of 4K inode size) ... in one block...
in Peter's case .. 1 MB block would hold 512 inodes...

the total number of allocated file system  blocks of the inode file is a bit more complex ... off topic here

to be clear .. the waste of space  does not come from  having small inode size/or mismatch of subblocksize ... itself..  the worst case (which is negligible) there is n unused fragment

its more.. that small file's data can't  (or less likely) written into the inode (data in inode) .. (( please note the good remark from Ed , only possible at all, - if there is no encryption ))
so in Peter's case .. a file , that has , lets say 2.x KB ...  can't be written into the inode... and so a file system block needs to be allocated..
if it is a new file.. a full  block  gets allocated first and then, on close of the file.. the size will be truncated to the next matching sub blocksize boundary

so .. performance wise.. that adds latency   and space wise.. this could be avoided .. (if the file's data fits into the inode)

to be more accurate and correct, the best answer would have been .. it depends 😉 ..   on the data structure...



Am 02. 08. 2023 um 13: 42 schrieb Olaf Weiser <olaf. weiser@ de. ibm. com>: Hallo Peter, [1] [. . . ] having a smaller inode size than the subblock size means there's a big wastage on disk usage, with no performance benefit to doing so[. . . ] in
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Am 02.08.2023 um 13:42 schrieb Olaf Weiser <olaf.weiser at de.ibm.com>:

Hallo Peter,

[1] [...] having a smaller inode size than the subblock size means there's a big wastage on disk usage, with no performance benefit to doing so[...]
in short - yes 😉



The expectation that there is a waste in space seems to come from the idea that inodes are stored as individual files - which then can’t be smaller than a subblock.

Referring to:

<https://www.ibm.com/blogs/digitale-perspektive/wp-content/uploads/2020/03/04-SSSD20-SpectrumScale-Konzepte-Teil2-032020.pdf>
[Vorschau.png]
04-SSSD20-SpectrumScale-Konzepte-Teil2-032020<https://www.ibm.com/blogs/digitale-perspektive/wp-content/uploads/2020/03/04-SSSD20-SpectrumScale-Konzepte-Teil2-032020.pdf>
PDF-Dokument · 1,2 MB<https://www.ibm.com/blogs/digitale-perspektive/wp-content/uploads/2020/03/04-SSSD20-SpectrumScale-Konzepte-Teil2-032020.pdf>


Slide 21: „Held in one invisible inode file…“

-> I would understand from that that 2kiB inodes are just ligned up in a single file and worst case you lose 2kiB because you don’t completely match your 4kiB inodes

Jan


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Von: gpfsug-discuss <gpfsug-discuss-bounces at gpfsug.org> im Auftrag von Jan Heichler <jan.heichler at gmx.net>
Gesendet: Mittwoch, 2. August 2023 15:09
An: gpfsug main discussion list <gpfsug-discuss at gpfsug.org>
Betreff: [EXTERNAL] Re: [gpfsug-discuss] Inode size, and system pool subblock

Am 02. 08. 2023 um 13: 42 schrieb Olaf Weiser <olaf. weiser@ de. ibm. com>: Hallo Peter, [1] [. . . ] having a smaller inode size than the subblock size means there's a big wastage on disk usage, with no performance benefit to doing so[. . . ] in
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Am 02.08.2023 um 13:42 schrieb Olaf Weiser <olaf.weiser at de.ibm.com>:

Hallo Peter,

[1] [...] having a smaller inode size than the subblock size means there's a big wastage on disk usage, with no performance benefit to doing so[...]
in short - yes 😉



The expectation that there is a waste in space seems to come from the idea that inodes are stored as individual files - which then can’t be smaller than a subblock.

Referring to:

<https://www.ibm.com/blogs/digitale-perspektive/wp-content/uploads/2020/03/04-SSSD20-SpectrumScale-Konzepte-Teil2-032020.pdf>
[Vorschau.png]
04-SSSD20-SpectrumScale-Konzepte-Teil2-032020<https://www.ibm.com/blogs/digitale-perspektive/wp-content/uploads/2020/03/04-SSSD20-SpectrumScale-Konzepte-Teil2-032020.pdf>
PDF-Dokument · 1,2 MB<https://www.ibm.com/blogs/digitale-perspektive/wp-content/uploads/2020/03/04-SSSD20-SpectrumScale-Konzepte-Teil2-032020.pdf>


Slide 21: „Held in one invisible inode file…“

-> I would understand from that that 2kiB inodes are just ligned up in a single file and worst case you lose 2kiB because you don’t completely match your 4kiB inodes

Jan

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