# CCTM output file is limited to 4GB

**URL:** <https://forum.cmascenter.org/t/cctm-output-file-is-limited-to-4gb/1859>\
**Category:** CMAQ\
**Created:** [October 23, 2020, 2:30am UTC](https://forum.cmascenter.org/t/cctm-output-file-is-limited-to-4gb/1859 "2020-10-23T02:30:24Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Nguyen\_Dong](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.cmascenter.org/nguyen_dong/32/67_2.png) [@Nguyen\_Dong](https://forum.cmascenter.org/u/Nguyen_Dong)\
**Post date:** [October 23, 2020, 2:30am UTC](https://forum.cmascenter.org/t/cctm-output-file-is-limited-to-4gb/1859/1 "2020-10-23T02:30:24Z")

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Hi everyone.

Currently I am using CMAQ 5.3, the resulting file from my cctm is limited to 4gb.  
How to remove this limit, please guide.

Thanks you.

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**Author:** ![cjcoats](https://avatars.discourse-cdn.com/v4/letter/c/ac8455/32.png) [@cjcoats](https://forum.cmascenter.org/u/cjcoats)\
**Post date:** [October 23, 2020, 10:41am UTC](https://forum.cmascenter.org/t/cctm-output-file-is-limited-to-4gb/1859/2 "2020-10-23T10:41:09Z")

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Whici I/O API version and netCDF version are you using? In your script, do

`setenv IOAPI_OFFSET_64 YES`

(this is the default for I/O API 3.2 with netCDF 3.6.2 or later)

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**Author:** ![Nguyen\_Dong](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.cmascenter.org/nguyen_dong/32/67_2.png) [@Nguyen\_Dong](https://forum.cmascenter.org/u/Nguyen_Dong)\
**Post date:** [October 23, 2020, 1:10pm UTC](https://forum.cmascenter.org/t/cctm-output-file-is-limited-to-4gb/1859/3 "2020-10-23T13:10:24Z")

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Hi cjcoats.  
I use I/O API 3.2 and netCDF 4.7.  
In my script have IOAPI\_OFFSET\_64 YES.

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**Author:** ![cjcoats](https://avatars.discourse-cdn.com/v4/letter/c/ac8455/32.png) [@cjcoats](https://forum.cmascenter.org/u/cjcoats)\
**Post date:** [October 23, 2020, 2:04pm UTC](https://forum.cmascenter.org/t/cctm-output-file-is-limited-to-4gb/1859/4 "2020-10-23T14:04:36Z")

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Curious.  
I’ve got along fine with files as large as 1.2 TB (33-year LSM/hydrology runs, and that with I/O API 3.1, where I needed an explicit ` IOAPI_OFFSET_64 YES`)…

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**Author:** ![cjcoats](https://avatars.discourse-cdn.com/v4/letter/c/ac8455/32.png) [@cjcoats](https://forum.cmascenter.org/u/cjcoats)\
**Post date:** [October 23, 2020, 2:07pm UTC](https://forum.cmascenter.org/t/cctm-output-file-is-limited-to-4gb/1859/5 "2020-10-23T14:07:37Z")

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Wait a minute… is an _individual timestep total volume_ that large? For that, you need to compile everthing (CMAQ + I/O API) with the “medium” memory model (see [https://cjcoats.github.io/ioapi/AVAIL.html#medium](https://cjcoats.github.io/ioapi/AVAIL.html#medium), and to be using netCDF-4

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<div class="post-metadata">

**Author:** ![Nguyen\_Dong](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.cmascenter.org/nguyen_dong/32/67_2.png) [@Nguyen\_Dong](https://forum.cmascenter.org/u/Nguyen_Dong)\
**Post date:** [October 23, 2020, 2:13pm UTC](https://forum.cmascenter.org/t/cctm-output-file-is-limited-to-4gb/1859/6 "2020-10-23T14:13:39Z")

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With my netCDF and WRF, I tested the big file and it was successful.