Re: random i/o error without error in dmesg

[Marc Joliet <marcec@gmx.de>]

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Hi

FWIW, this sounds like what I've been seeing with dovecot.  In case it's 
relevant, I'll try to explain.

After some uptime, I'll see log messages like this:

Okt 26 12:05:46 thetick dovecot[467]: imap(marcec): Error: pread() failed with 
file /home/marcec/.mdbox/mailboxes/BTRFS/dbox-Mails/dovecot.index.log: 
Input/output error

Occasionally they go away by themselves, but usually I have to reboot to make 
them go away.  This happens when getmail attempts to fetch mail, which fails 
due to the above error.  After the reboot getmail succeeds again.

As in Szalma's case, btrfs-scrub never reports anything wrong.

I use LZO compression on the relevant file system, so I wanted to wait until 
kernel 4.1.11 before reporting this, but that hasn't hit Gentoo yet (and 
neither has 4.1.10, for some reason).  I don't use quotas.

According to the what I see in the systemd journal, the errors started on 
2015-06-01 with kernel 3.19.8.  Note that, strangely enough, I had been using 
that same version since 2015-05-23, so for more than a week before the error 
cropped up.  I checked whether I made any changes to the configuration, and 
found this:

diff --git a/kernels/kernel-config-3.19.8-gentoo b/kernels/kernel-
config-3.19.8-gentoo
index b061b31..8cf8eba 100644
--- a/kernels/kernel-config-3.19.8-gentoo
+++ b/kernels/kernel-config-3.19.8-gentoo
@@ -64,7 +64,7 @@ CONFIG_INIT_ENV_ARG_LIMIT=32
 CONFIG_CROSS_COMPILE=""
 # CONFIG_COMPILE_TEST is not set
 CONFIG_LOCALVERSION=""
-CONFIG_LOCALVERSION_AUTO=y
+# CONFIG_LOCALVERSION_AUTO is not set
 CONFIG_HAVE_KERNEL_GZIP=y
 CONFIG_HAVE_KERNEL_BZIP2=y
 CONFIG_HAVE_KERNEL_LZMA=y
@@ -73,8 +73,8 @@ CONFIG_HAVE_KERNEL_LZO=y
 CONFIG_HAVE_KERNEL_LZ4=y
 # CONFIG_KERNEL_GZIP is not set
 # CONFIG_KERNEL_BZIP2 is not set
-CONFIG_KERNEL_LZMA=y
-# CONFIG_KERNEL_XZ is not set
+# CONFIG_KERNEL_LZMA is not set
+CONFIG_KERNEL_XZ=y
 # CONFIG_KERNEL_LZO is not set
 # CONFIG_KERNEL_LZ4 is not set
 CONFIG_DEFAULT_HOSTNAME="(none)"
@@ -132,7 +132,7 @@ CONFIG_TICK_CPU_ACCOUNTING=y
 # CONFIG_VIRT_CPU_ACCOUNTING_GEN is not set
 # CONFIG_IRQ_TIME_ACCOUNTING is not set
 CONFIG_BSD_PROCESS_ACCT=y
-# CONFIG_BSD_PROCESS_ACCT_V3 is not set
+CONFIG_BSD_PROCESS_ACCT_V3=y
 CONFIG_TASKSTATS=y
 CONFIG_TASK_DELAY_ACCT=y
 CONFIG_TASK_XACCT=y

The only change I can think of that might affect anything is 
CONFIG_BSD_PROCESS_ACCT_V3=y (I don't remember why exactly I set it).  I can 
try without it set, but maybe the kernel configuration is a red herring?

Anyway, the current state of the system is:

# uname -r 
4.1.9-gentoo-r1
# btrfs filesystem show / 
Label: 'MARCEC_ROOT'  uuid: 0267d8b3-a074-460a-832d-5d5fd36bae64
        Total devices 1 FS bytes used 74.40GiB
        devid    1 size 107.79GiB used 105.97GiB path /dev/sda1

btrfs-progs v4.2.2
# btrfs filesystem df /
Data, single: total=98.94GiB, used=72.30GiB
System, single: total=32.00MiB, used=20.00KiB
Metadata, single: total=7.00GiB, used=2.10GiB
GlobalReserve, single: total=512.00MiB, used=0.00B

The filesystem is mounted as (leaving out subvolume mounts which use the same 
mount options):
/dev/sda1 on / type btrfs (rw,noatime,compress=lzo,ssd,discard,space_cache)

Greetings,
-- 
Marc Joliet
--
"People who think they know everything really annoy those of us who know we
don't" - Bjarne Stroustrup

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