# I/O error

**URL:** <https://forums.suse.com/t/i-o-error/34579>\
**Category:** SLES Hardware\
**Created:** [November 25, 2019, 3:34pm UTC](https://forums.suse.com/t/i-o-error/34579 "2019-11-25T15:34:19Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![suseluckycement](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@suseluckycement](https://forums.suse.com/u/suseluckycement)\
**Post date:** [November 25, 2019, 3:34pm UTC](https://forums.suse.com/t/i-o-error/34579/1 "2019-11-25T15:34:19Z")

</div>

OS: SLES 12 for SAP SP 3 + fully updated/patched.

Once in a week, System(application and Database) becomes unresponsive due to I/O error.  
While having I/O error, we can ping and access the system via SSH/PuTTY, though none of the standard linux command runs successfully due to I/O error:

:~ # top  
:~ # /usr/bin/top: Input/output error  
:~ # dmesg  
:~ # /usr/bin/dmesg: Input/output error  
:~ # tail -f /var/log/messages  
:~ # /usr/bin/tail: Input/output error

The interesting part is that issue always gets fixed(for next 4-5 days) simply by hard rebooting the server(system didnt even reboots via command) and system keeps running without any issue till next I/O error(repeats every 5-6 days).

No single FS error is every reported(in the logs) on this system. We even run the file system checks too.

SUSE Support advised us

> [@](#):
>
> There is no errors or messages indicating issue on the file system level so far. I/O errors are not only related to File system.  
> By looking at the logs, it seems the memory cached keeps increasing and its not getting freed. I would recommend to tune up the memory as indicated in the TID below :  
> [https://www.suse.com/support/kb/doc/?id=7021211](https://www.suse.com/support/kb/doc/?id=7021211)
> 
> Please let me know once this is done and send me a new supportconfig.
> 
> We will then monitor the server behavior.

I am unable to understand how memory tuning would prevent the I/O error ? Interestingly this is the SAP HANA replication target, i.e this system is a Passive node, while we never ever face I/O errors on Master/Primary SAP Server.

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<div class="post-metadata">

**Author:** ![suseluckycement](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@suseluckycement](https://forums.suse.com/u/suseluckycement)\
**Post date:** [November 25, 2019, 3:51pm UTC](https://forums.suse.com/t/i-o-error/34579/2 "2019-11-25T15:51:37Z")

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```auto
# df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 252G 0 252G 0% /dev
tmpfs 393G 80K 393G 1% /dev/shm
tmpfs 252G 9.9M 252G 1% /run
tmpfs 252G 0 252G 0% /sys/fs/cgroup
/dev/sda4 788G 266G 522G 34% /
/dev/sda2 985M 74M 860M 8% /boot
/dev/sda6 1.0T 28G 997G 3% /hana/log
/dev/sda7 297G 24G 273G 8% /hana/shared
/dev/sda5 2.0T 321G 1.7T 16% /hana/data
tmpfs 51G 0 51G 0% /run/user/485
tmpfs 51G 0 51G 0% /run/user/1000
tmpfs 51G 0 51G 0% /run/user/1006
tmpfs 51G 16K 51G 1% /run/user/487
tmpfs 51G 0 51G 0% /run/user/1004

# /usr/bin/free -h
             total used free shared buffers cached
Mem: 503G 140G 363G 7.5G 85M 8.9G
-/+ buffers/cache: 131G 372G
Swap: 20G 0B 20G

```

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<div class="post-metadata">

**Author:** ![malcolmlewis](https://sea2.discourse-cdn.com/flex022/user_avatar/forums.suse.com/malcolmlewis/32/11375_2.png) [@malcolmlewis](https://forums.suse.com/u/malcolmlewis)\
**Post date:** [November 25, 2019, 5:17pm UTC](https://forums.suse.com/t/i-o-error/34579/3 "2019-11-25T17:17:36Z")

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Hi  
With that amount of memory available, consider tweaking any swap usage?

I use;

```auto
cat /etc/sysctl.d/98-grover.conf

#disable swap
vm.swappiness=1
vm.vfs_cache_pressure=50
```

This will ensure RAM is actually used before hitting the swap space.

So disks are all ok, memory has all been tested, filesystem checks run?

Have you run iotop rather than top, I would leave it (iotop) running in a session…

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<div class="post-metadata">

**Author:** ![suseluckycement](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@suseluckycement](https://forums.suse.com/u/suseluckycement)\
**Post date:** [November 26, 2019, 9:09am UTC](https://forums.suse.com/t/i-o-error/34579/4 "2019-11-26T09:09:59Z")

</div>

Nice advise, however I am interested to know if Tuning Memory would possibly prevent I/O error to occur ? For me its hard to imagine.

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<div class="post-metadata">

**Author:** ![malcolmlewis](https://sea2.discourse-cdn.com/flex022/user_avatar/forums.suse.com/malcolmlewis/32/11375_2.png) [@malcolmlewis](https://forums.suse.com/u/malcolmlewis)\
**Post date:** [November 26, 2019, 3:29pm UTC](https://forums.suse.com/t/i-o-error/34579/5 "2019-11-26T15:29:00Z")

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> [@suseluckycement;58933](#):
>
> Nice advise, however I am interested to know if Tuning Memory would possibly prevent I/O error to occur ? For me its hard to imagine.

Hi  
Hi  
Well is the system swapping when i/o issues occur? Have you checked the disks and filesystems as well as the RAM?

Running iotop may give a better indication of what is happening.