# The Month of Problems

For over a month I had problem with my Synlogy Diskstation 416play. After a few hours of usage the Diskstation became sluggish, unresponsive and eventually froze up. If I noticed in time I could quickly reboot the system via ssh. The web interface usually didn't work at that point any more. However if I didn't notice early enough then all that was left was pressing the power button for 8 seconds to reboot the system.

Not a good solution as that leads to a RAID parity check.

If you look at the CPU, memory and I/O statistics of the last month you can see the down times quite clearly:

<TABLE>
  <TR>
    <TD>
        <P><IMG SRC="https://files.steempeak.com/file/steempeak/krischik/qd9ji1h5-Screenshot20at20Sep20102016-43-27.png"></P>
    </TD>
    <TD>
      <P><IMG SRC="https://files.steempeak.com/file/steempeak/krischik/AcS1WKxV-Screenshot20at20Sep20102016-45-54.png"></P>
    </TD>
  </TR>
  <TR>
    <TD >
        <P>Physical Memory in %</P>
    </TD>
    <TD>
      <P>Swap Memory in I/O operations</P>
    </TD>
  </TR>
  <TR>
    <TD>
        <P><IMG SRC="https://files.steempeak.com/file/steempeak/krischik/AGryKVlT-Screenshot20at20Sep20102019-16-49.png"></P>
    </TD>
    <TD>
      <P><IMG SRC="https://files.steempeak.com/file/steempeak/krischik/G12LQFmt-Screenshot20at20Sep20102019-20-16.png"></P>
    </TD>
  </TR>
  <TR>
    <TD>
        <P>CPU usage in %</P>
    </TD>
    <TD>
      <P>Volume I/O in %</P>
    </TD>
  </TR>
</TABLE>

Whenever the values show zero the system was basically frozen. I call it frozen as the system wasn't responding. However, the hard-drives where still in full use. But whatever the system was doing it wasn't anything useful as not even the statistical data was saved any more.

# Switching off Services

In order to keep the system running I switched off all non essential services and one by one started them again. In the end the system was halfway stable without index service, Moments, Synlogy Drive Server, Synlogy Office, Hyper Backup and **SMB / AFP connection**.

But with that many essential services, including the SMB / AFP connection, deactivated the system wasn't very helpful any more. I had to find a proper fix.

# Adding more Memory

Throughout the month I was looking for a solution, Tried difference combination services to activate. Doubling `vm.min_free_kbytes` as that was mentioned as a fix. But nothing helped. Until i finally found a community posting mentioning installing more memory. Increasing memory from 1GB to 8GB to be precise. The Memory used by the 416play is not that expensive, warranty has expired, so I ordered a **KINGSTON 8 GB DDR3L-SDRAM SO-DIMM 204-Pin**.

With the aid of one of the many [guide on the internet](https://www.reddit.com/r/synology/comments/5s5kyr/tutorial_upgrading_your_synology_ds416play_to_8gb/) I replaced the memory in less than an hour. Taking the case apart is the most difficult.

<TABLE>
  <TR>
    <TD>
        <P><IMG SRC="https://files.steempeak.com/file/steempeak/krischik/LLPab1Ew-20190911_070919.jpg"></P>
    </TD>
  </TR>
  <TR>
    <TD>
        <P>Synlogy knows precisely what part is in desperate need of an upgrade.</P>
    </TD>
  </TR>
</TABLE>

And the result: Everything is working again and better than it ever did before. All services started again, including Moments and indexing, which had been the biggest trouble maker in the past, and everything is working smoothly.

# A Closer Look at the Current Statistic

With this success I took a closer look at the memory usage of the currently running system:

<TABLE>
  <TR>
    <TD>
        <P><IMG SRC="https://files.steempeak.com/file/steempeak/krischik/PIo6XbGK-Screenshot20at20Sep20102016-53-00.png"></P>
    </TD>
  </TR>
  <TR>
    <TD>
        <P>Physical Memory in usage</P>
    </TD>
  </TR>
  <TR>
    <TD>
        <P><IMG SRC="https://files.steempeak.com/file/steempeak/krischik/OpJdnFgD-Screenshot20at20Sep20102016-47-06.png"></P>
    </TD>
  </TR>
  <TR>
    <TD>
        <P>Swapper in I/O and usage</P>
    </TD>
  </TR>
</TABLE>

The swapper is, as expected after adding eight time the memory, empty so only main memory is of interest. The yellow part is the memory actually used by the apps. With that 2.5GB this is 2½ times the total memory originally installed.

I have worked with swapper ever since they where invented in the 1980th. And ever since then they have been a constant pain.

When introduced in the 1980th swapper where advertised as a great way to expand expensive main memory to become virtually limitless by use of cheap hard drive memory.

But that is not true. In my 30 years of experience I have learned that the swapper can at best double your memory. Once more data is stored in the swapper then main memory system performance degrades significantly. And once the swapper exceeds twice the main memory (⅓ of data is stored in main memory and ⅔ in the swapper) death by swapping will follow soon — that is the system becomes unusable.

That Synlogy added 6GB of swapper to a computer with only 1GB main memory is pointless. The system died by swapping long before the 6GB filled up.

From this one might be tempted to think that 4GB is enough and one could save some money when extending  their system. That has some merit but I like to direct you to the 5.1 GB memory marked in dark green. That's the hard drive cache. The Diskstation is a NAS and providing data from the hard drive is its main job. With a such a huge hard drive cache data is provided that much faster.

# Current status

Let's look at the table from before but instead of last month only from today:

<TABLE>
  <TR>
    <TD>
        <P><IMG SRC="https://files.steempeak.com/file/steempeak/krischik/WkxFZdgN-Screenshot20at20Sep20102018-39-40.png"></P>
    </TD>
    <TD>
      <P><IMG SRC="https://files.steempeak.com/file/steempeak/krischik/dcCZqthI-Screenshot20at20Sep20102018-40-17.png"></P>
    </TD>
  </TR>
  <TR>
    <TD>
        <P>Physical Memory in %</P>
    </TD>
    <TD>
        <P>Swap Memory in I/O operations</P>
    </TD>
  </TR>
  <TR>
    <TD>
        <P><IMG SRC="https://files.steempeak.com/file/steempeak/krischik/S5IVGnD8-Screenshot20at20Sep20102019-17-42.png"></P>
    </TD>
    <TD>
      <P><IMG SRC="https://files.steempeak.com/file/steempeak/krischik/JiPAmHNL-Screenshot20at20Sep20102019-20-51.png"></P>
    </TD>
  </TR>
  <TR>
    <TD>
        <P>CPU usage in %</P>
    </TD>
    <TD>
      <P>Volume I/O in %</P>
    </TD>
  </TR>
</TABLE>

You can see that the system has frozen over night and was rebooted shortly before 7 o'Clock. You can also see that the system was shut down at about 15 o'Clock to install the new memory.

Main memory usage dropped 65% (of 1GB) to 30% (of 8GB). The system never used all the system memory for applications. Even before some was used as hard drive cache. Which means that from the 2.5GB of application memory needed only ¼ was keep in main memory.

Swap I/O dropped to zero as those 6GB of swapper is not unused any more. Which is perfect. For best performance the swapper should only be used in exceptional circumstance. Mind you, I tried using systems with lots of main memory and swapper deactivated but that turned out to be not a good idea. It's OK to have those 6GB do nothing.

CPU usage increased which is also no surprise. With only 1GB even the relatively weak Celeron N3060 was waiting for memory to be swapped in and out most of the time.

Which brings us to volume I/O which changed from 100% choke block to a more healthy 50%. That all look very promising.

I do suspect now that it was indeed the `vm.min_free_kbytes` filling up. This memory is used to provide emergency memory to interrupt handler and will indeed freeze the system if there is nothing left. Doubling `vm.min_free_kbytes` form 64MB to 128 MB (⅛ of 1GB) did not help and doubling yet again wasn't really an option on a system with only 1GB of memory.

# Conclusion

Right now the memory increase was an absolute success. It seems that 8GB is the perfect amount of memory to have you Diskstation run absolutely smoothly. But 4GB will probably work as well.

Of course I have to see how it goes for another week to be absolutely sure my problems are gone. Updates in the comment. Knock on wood.

<center>![](https://www.synology.com/img/products/detail/DS416play/heading.png)</center>

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