Why is most the of disk IO attributed to jbd2 and not to the process that is actually using the IO?
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When monitoring disk IO, most of the IO is attributed to jbd2, while the original process that caused the high IO is attributed a much lower IO percentage. Why?
Here's iotop's example output (other processes with IO<1% omitted):
process io disk
edited Feb 4 at 2:37
Boann
1677
asked Feb 8 '17 at 23:24
SparklerSparkler
3291313
add a comment |
When monitoring disk IO, most of the IO is attributed to jbd2, while the original process that caused the high IO is attributed a much lower IO percentage. Why?
Here's iotop's example output (other processes with IO<1% omitted):
process io disk
edited Feb 4 at 2:37
Boann
1677
asked Feb 8 '17 at 23:24
SparklerSparkler
3291313
Is this withdata=journal?
– DepressedDaniel
Feb 9 '17 at 0:00
@DepressedDaniel not sure what you mean. I just used iotop -oP
– Sparkler
Feb 9 '17 at 0:01
add a comment |
When monitoring disk IO, most of the IO is attributed to jbd2, while the original process that caused the high IO is attributed a much lower IO percentage. Why?
Here's iotop's example output (other processes with IO<1% omitted):
process io disk
edited Feb 4 at 2:37
Boann
1677
asked Feb 8 '17 at 23:24
SparklerSparkler
3291313
When monitoring disk IO, most of the IO is attributed to jbd2, while the original process that caused the high IO is attributed a much lower IO percentage. Why?
Here's iotop's example output (other processes with IO<1% omitted):
process io disk
process io disk
edited Feb 4 at 2:37
Boann
1677
asked Feb 8 '17 at 23:24
SparklerSparkler
3291313
edited Feb 4 at 2:37
Boann
1677
asked Feb 8 '17 at 23:24
SparklerSparkler
3291313
edited Feb 4 at 2:37
Boann
1677
edited Feb 4 at 2:37
Boann
1677
edited Feb 4 at 2:37
Boann
1677
1677
asked Feb 8 '17 at 23:24
SparklerSparkler
3291313
asked Feb 8 '17 at 23:24
SparklerSparkler
3291313
asked Feb 8 '17 at 23:24
SparklerSparkler
3291313
3291313
Is this withdata=journal?
– DepressedDaniel
Feb 9 '17 at 0:00
@DepressedDaniel not sure what you mean. I just used iotop -oP
– Sparkler
Feb 9 '17 at 0:01
add a comment |
Is this withdata=journal?
– DepressedDaniel
Feb 9 '17 at 0:00
@DepressedDaniel not sure what you mean. I just used iotop -oP
– Sparkler
Feb 9 '17 at 0:01
Is this with
data=journal?– DepressedDaniel
Feb 9 '17 at 0:00
Is this with
data=journal?– DepressedDaniel
Feb 9 '17 at 0:00
@DepressedDaniel not sure what you mean. I just used iotop -oP
– Sparkler
Feb 9 '17 at 0:01
@DepressedDaniel not sure what you mean. I just used iotop -oP
– Sparkler
Feb 9 '17 at 0:01
add a comment |
1 Answer
1
active
oldest
votes
jbd2 is a kernel thread that updates the filesystem journal.
Tracing filesystem or disk activity with the process that caused it is difficult because the activities of many processes are combined together. For example, if two processes are reading from the same file at the same time, which process would the read be accounted against? If two processes write to the same directory and the directory is updated on disk only once (combining the two operations), which process would the write be accounted against?
In your case, it appears that most of the traffic consists of updates to the journal. This is traced to the journal updater, but there's no tracing between journal updates and the process(es) that caused the write operation(s) that required this journal update.
answered Feb 9 '17 at 0:39
GillesGilles
539k12810891606
1
Which other disk io categories are there besides journal updates? (i.e. why jdb2 is not the only entry in iotop's output?)
– Sparkler
Feb 9 '17 at 1:33
@Sparkler There's writing the actual data, as well. (Unless you're using a log-structured filesystem, but most aren't.)
– Gilles
Feb 9 '17 at 10:25
That explains what happens. But it sucks big time when the original process' I/O priority has been set to 'idle' andjbd2just continues doing lots of I/O at its own I/O priority.
– jlh
Dec 31 '18 at 17:37
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
jbd2 is a kernel thread that updates the filesystem journal.
Tracing filesystem or disk activity with the process that caused it is difficult because the activities of many processes are combined together. For example, if two processes are reading from the same file at the same time, which process would the read be accounted against? If two processes write to the same directory and the directory is updated on disk only once (combining the two operations), which process would the write be accounted against?
In your case, it appears that most of the traffic consists of updates to the journal. This is traced to the journal updater, but there's no tracing between journal updates and the process(es) that caused the write operation(s) that required this journal update.
answered Feb 9 '17 at 0:39
GillesGilles
539k12810891606
1
Which other disk io categories are there besides journal updates? (i.e. why jdb2 is not the only entry in iotop's output?)
– Sparkler
Feb 9 '17 at 1:33
@Sparkler There's writing the actual data, as well. (Unless you're using a log-structured filesystem, but most aren't.)
– Gilles
Feb 9 '17 at 10:25
That explains what happens. But it sucks big time when the original process' I/O priority has been set to 'idle' andjbd2just continues doing lots of I/O at its own I/O priority.
– jlh
Dec 31 '18 at 17:37
add a comment |
jbd2 is a kernel thread that updates the filesystem journal.
Tracing filesystem or disk activity with the process that caused it is difficult because the activities of many processes are combined together. For example, if two processes are reading from the same file at the same time, which process would the read be accounted against? If two processes write to the same directory and the directory is updated on disk only once (combining the two operations), which process would the write be accounted against?
In your case, it appears that most of the traffic consists of updates to the journal. This is traced to the journal updater, but there's no tracing between journal updates and the process(es) that caused the write operation(s) that required this journal update.
answered Feb 9 '17 at 0:39
GillesGilles
539k12810891606
1
Which other disk io categories are there besides journal updates? (i.e. why jdb2 is not the only entry in iotop's output?)
– Sparkler
Feb 9 '17 at 1:33
@Sparkler There's writing the actual data, as well. (Unless you're using a log-structured filesystem, but most aren't.)
– Gilles
Feb 9 '17 at 10:25
That explains what happens. But it sucks big time when the original process' I/O priority has been set to 'idle' andjbd2just continues doing lots of I/O at its own I/O priority.
– jlh
Dec 31 '18 at 17:37
add a comment |
jbd2 is a kernel thread that updates the filesystem journal.
Tracing filesystem or disk activity with the process that caused it is difficult because the activities of many processes are combined together. For example, if two processes are reading from the same file at the same time, which process would the read be accounted against? If two processes write to the same directory and the directory is updated on disk only once (combining the two operations), which process would the write be accounted against?
In your case, it appears that most of the traffic consists of updates to the journal. This is traced to the journal updater, but there's no tracing between journal updates and the process(es) that caused the write operation(s) that required this journal update.
answered Feb 9 '17 at 0:39
GillesGilles
539k12810891606
jbd2 is a kernel thread that updates the filesystem journal.
Tracing filesystem or disk activity with the process that caused it is difficult because the activities of many processes are combined together. For example, if two processes are reading from the same file at the same time, which process would the read be accounted against? If two processes write to the same directory and the directory is updated on disk only once (combining the two operations), which process would the write be accounted against?
In your case, it appears that most of the traffic consists of updates to the journal. This is traced to the journal updater, but there's no tracing between journal updates and the process(es) that caused the write operation(s) that required this journal update.
answered Feb 9 '17 at 0:39
GillesGilles
539k12810891606
answered Feb 9 '17 at 0:39
GillesGilles
539k12810891606
answered Feb 9 '17 at 0:39
GillesGilles
539k12810891606
answered Feb 9 '17 at 0:39
GillesGilles
539k12810891606
539k12810891606
1
Which other disk io categories are there besides journal updates? (i.e. why jdb2 is not the only entry in iotop's output?)
– Sparkler
Feb 9 '17 at 1:33
@Sparkler There's writing the actual data, as well. (Unless you're using a log-structured filesystem, but most aren't.)
– Gilles
Feb 9 '17 at 10:25
That explains what happens. But it sucks big time when the original process' I/O priority has been set to 'idle' andjbd2just continues doing lots of I/O at its own I/O priority.
– jlh
Dec 31 '18 at 17:37
add a comment |
1
Which other disk io categories are there besides journal updates? (i.e. why jdb2 is not the only entry in iotop's output?)
– Sparkler
Feb 9 '17 at 1:33
@Sparkler There's writing the actual data, as well. (Unless you're using a log-structured filesystem, but most aren't.)
– Gilles
Feb 9 '17 at 10:25
That explains what happens. But it sucks big time when the original process' I/O priority has been set to 'idle' andjbd2just continues doing lots of I/O at its own I/O priority.
– jlh
Dec 31 '18 at 17:37
1
1
Which other disk io categories are there besides journal updates? (i.e. why jdb2 is not the only entry in iotop's output?)
– Sparkler
Feb 9 '17 at 1:33
Which other disk io categories are there besides journal updates? (i.e. why jdb2 is not the only entry in iotop's output?)
– Sparkler
Feb 9 '17 at 1:33
@Sparkler There's writing the actual data, as well. (Unless you're using a log-structured filesystem, but most aren't.)
– Gilles
Feb 9 '17 at 10:25
@Sparkler There's writing the actual data, as well. (Unless you're using a log-structured filesystem, but most aren't.)
– Gilles
Feb 9 '17 at 10:25
That explains what happens. But it sucks big time when the original process' I/O priority has been set to 'idle' and
jbd2 just continues doing lots of I/O at its own I/O priority.– jlh
Dec 31 '18 at 17:37
That explains what happens. But it sucks big time when the original process' I/O priority has been set to 'idle' and
jbd2 just continues doing lots of I/O at its own I/O priority.– jlh
Dec 31 '18 at 17:37
add a comment |
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Is this with
data=journal?– DepressedDaniel
Feb 9 '17 at 0:00
@DepressedDaniel not sure what you mean. I just used iotop -oP
– Sparkler
Feb 9 '17 at 0:01