Putting .system to an SD-Card

[Freakazoid]

Hello there,

in order to being able to spindown my HDDs, I'd like to put the .system log file to an external medium. I read about the concerns when using an USB flash drive for this purpose. Thats's why I'm thinking about using an industrial grade SD card. Before I do so, I have some questions

1. Is the speed of the SD card a critical thing for the overall performance of the NAS?
2. What size is the .system file? What size of SD card should I buy?
3. Which card reader is recommended?
4. Any other issues concerning my approach?

Thanks for your help :)

 

[dlavigne]

I assume you mean the system dataset (http://doc.freenas.org/9.10/freenas_system.html#system-dataset)? If so, the size will depend upon what you store on it (see that section of the docs for what can be stored there) and how the system is used (eg are there a lot of errors, a large user/group cache, a lot of reporting info, etc.).

 

[Freakazoid]

Yes, thats what I meant.

 

[Freakazoid]

Any other oppinions/concerns/experiences?

 

[hugovsky]

I think you will kill any card in no time. .system writes are almost constant. Take that into consideration.

 

[Freakazoid]

How much data is written (e.g. per day) on an average NAS for home usage? The cards have a TBW of 192. Is there a way to minimize write cycles of the file?

 

[Ericloewe]

How much data is written (e.g. per day) on an average NAS for home usage? The cards have a TBW of 192. Is there a way to minimize write cycles of the file?

This is what it looks like with the server doing absolutely nothing user-facing.

Note that it's RAIDZ2, so multiply a single drive's workload by four to get a decent estimate for a single SD card.

 

[Freakazoid]

Thank you Ericloewe. So in your setup, there are around 200MB (45 MB * 4 as you mentioned) written per hour. In a day this would be 4.8 GB. That would be 1752 GB per year. Let's round this to 2 TB. The manufacturer of the card sells them with a TBW of _up to_ 192. Let's assume the average is about 100 to be on the safe(r) side. That would mean, the card would last for 50 years. That would be enough for me :).

Am I wrong in my thinking?

*Edit:
ATP has detailed information about their TBW values fot different card sizes: http://www.logicio.com/files/ATP Industrial grade microSD_spec_detail v3.3_20120920.pdf
So TBWs are not as high as I stated above, but I think they are still enough.

 

[CookiesLikeWhoa]

Does it change if the server is doing something? His numbers reflected the sever just "ideling".

I figure that you would want to take that into account as well.

 

[Luisgp]

Maybe an small sata SSD connected to usb with an adapter? could this be a supported configuration?

 

[Ericloewe]

Does it change if the server is doing something? His numbers reflected the sever just "ideling".

I figure that you would want to take that into account as well.

Expect additional logging from shares, jails and whatever you may be doing.

 

[Freakazoid]

I think I'm going to give it a try. Are there any specifically unsupported card readers?

 

[Ericloewe]

I think I'm going to give it a try. Are there any specifically unsupported card readers?

Not that we know of... Any USB Mass Storage Class SD card reader should work.

 

[Freakazoid]

Not that we know of... Any USB Mass Storage Class SD card reader should work.

Great. And is there a way to minimize the write load to the card? Like disabling some logging?

 

[Ericloewe]

Great. And is there a way to minimize the write load to the card? Like disabling some logging?

If you really want to do that, there's a checkbox in the .system dataset options.

 

[Freakazoid]

If you really want to do that, there's a checkbox in the .system dataset options.

Are there any downsides when using the checkbox other than harder troubleshooting?

 

[Ericloewe]

Are there any downsides when using the checkbox other than harder troubleshooting?

I don't think so, but that's a big one as it is.

IIRC, you also lose the reporting graphs on reboot.

 

[Freakazoid]

Okay great. I'll test everything soon and let you guys know how everything turned out. :)

Thanks for all of your help