SFSGLOBALIOLIMITS.CFG(5)

📦
version 5.8.0 · 4 versions
, in ubuntu stonking

💖 SFSGLOBALIOLIMITS.CFG 💖

okay bestie, so sfsglobaliolimits.cfg(5) is the manual page for sfsglobaliolimits.cfg — literally the config file that holds the settings for the global I/O limiter. yes, the thing that decides who gets how much bandwidth. it's giving traffic cop but make it filesystem. 🚦✨

🌸 NAME 🌸

sfsglobaliolimits.cfg — global I/O limiting configuration

💅 DESCRIPTION 💅

The file sfsglobaliolimits.cfg contains the configuration of the global I/O limiter. that's it. that's the whole vibe. it's the file. it configures the limiter. slay. 💖

✨ SYNTAX ✨

The syntax is, no cap, just:

option value

and any line that starts with the # character? ignored. ghosted. not even looked at. 🙈

🎀 OPTIONS 🎀

Here are the configuration options, bestie, one by one, no skips:

  • subsystem <subsystem> — the cgroups subsystem that clients get classified by. if you leave this unspecified, then literally all clients are considered unclassified (peep the next option for what that means 👀).
  • limit unclassified <throughput in KiB/s> — the special entry for clients that don't match any group listed in the config file, OR for every client if subsystem is unspecified. here's the tea though, and it's important:
    • if this entry is unspecified and subsystem is unspecified too, I/O limiting is disabled entirely — free-for-all, no limits, go wild.
    • if this entry is unspecified but subsystem is specified, then unclassified clients are not allowed to perform I/O. at all. nada. blocked. 💀
  • limit <group> <throughput in KiB/s> — sets the limit for clients that belong to the cgroups group <group>. and here's the plot twist: in SaunaFS, subgroups of <group> are independent groups. they are not allowed to use <group>'s bandwidth reservation, and they don't count against <group>'s usage. separate. sovereign. their own little kingdoms. 👑

🌈 EXAMPLES 🌈

example the first:

# empty file

I/O limiting is disabled, no limits are enforced. nothing. zero. the wild west. 🤠

example the second:

limit unclassified 1024

all clients are unclassified and they all share 1MiB/s of bandwidth. one big happy (throttled) family. 💖

example the third:

subsystem blkio
limit /a 1024

clients in the blkio /a group are limited to 1MiB/s, and no other clients can perform any I/O. sorry to everyone else. 😭

example the fourth (the iconic one):

subsystem blkio
limit unclassified 256
limit /a   1024
limit /b/a 2048

so the blkio group /a is allowed to transfer 1MiB/s, while /b/a gets 2MiB/s. and clients from other groups — like /b, /z, /a/a, /b/z — are considered unclassified and share 256KiB/s of bandwidth. yes, even /a/a! because subgroups are independent, remember? 👀 periodt.

🦋 TUNING NOTES 🦋

Global I/O limiting is managed by the master server. mount instances reserve bandwidth allocations from the master whenever they want to perform I/O to chunkservers.

to avoid overloading the master under heavy traffic, mounts try to predict their future usage and reserve, all at once, every bit of bandwidth they'll need for the next renegotiation period (see sfsmaster.cfg(5) — go read it, bestie, it's right there in SEE ALSO 🫶).

but here's the heartbreaking part: such reservations are wasted if the traffic at a given mount instance suddenly drops. just gone. evaporated. 💀

The ratio of bandwidth being wasted due to this phenomenon shouldn't exceed fsp/b, where:

  • f is the frequency of sudden traffic drops in the whole installation (in 1/s)
  • s is the average size of such drop (in KiB/s)
  • p is the renegotiation period (in s)
  • b is the bandwidth limit (in KiB/s)

and this applies to each group separately, because groups reserve their bandwidth independently from each other. they don't share, they don't coordinate, they mind their own business. 💅

😭 REPORTING BUGS 😭

Report bugs to the GitHub repository https://github.com/leil-io/saunafs as an issue. please and thank you. 🙏

Copyright 2008-2009 Gemius SA

Copyright 2013-2019 Skytechnology sp. z o.o.

Copyright 2023-2024 Leil Storage OÜ

SaunaFS is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 3.

SaunaFS is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with SaunaFS. If not, see http://www.gnu.org/licenses/.

🌟 SEE ALSO 🌟

and that's the whole page, bestie 🎀 this was SFSGLOBALIOLIMITS.CFG(5) from SaunaFS, dated 2026-07-29 — go forth and limit your I/O responsibly, mwah 💋✨

📦 where this page comes from