# VOLs and VFDs **URL:** https://forum.hdfgroup.org/c/hdf5/vols-vfds/7.md [Latest](https://forum.hdfgroup.org/latest.md) · [Categories](https://forum.hdfgroup.org/categories.md) --- ## [About the VOLs and VFDs category](https://forum.hdfgroup.org/t/about-the-vols-and-vfds-category/20)
**Author:** [@su-loric](https://forum.hdfgroup.org/u/su-loric)\ **Replies:** 0\ **Last updated:** [February 7, 2018, 11:11pm UTC](https://forum.hdfgroup.org/t/about-the-vols-and-vfds-category/20 "2018-02-07T23:11:26Z")
Post your questions regarding specific VFDs and VOLs as well as developing for the VFD and VOL layer here. --- ## [How exactly is async-i/o available in HDF5?](https://forum.hdfgroup.org/t/how-exactly-is-async-i-o-available-in-hdf5/13089)
**Author:** [@pphilippllucas](https://forum.hdfgroup.org/u/pphilippllucas)\ **Replies:** 16\ **Last updated:** [March 10, 2025, 5:35pm UTC](https://forum.hdfgroup.org/t/how-exactly-is-async-i-o-available-in-hdf5/13089 "2025-03-10T17:35:49Z")
Follow-Up to this thread I am still somewhat confused about how async-i/o is actually made available in HDF5. First up; I\`m tasked with evaluating the performance of different HDF5 features such as subfiling and async … --- ## [VOL-Async: Debugging Async operation failures](https://forum.hdfgroup.org/t/vol-async-debugging-async-operation-failures/13055)
**Author:** [@pphilippllucas](https://forum.hdfgroup.org/u/pphilippllucas)\ **Replies:** 12\ **Last updated:** [February 24, 2025, 5:33pm UTC](https://forum.hdfgroup.org/t/vol-async-debugging-async-operation-failures/13055 "2025-02-24T17:33:43Z")
(Deleted my previous post as I realize my failure analysis was false) I’ve been tasked with evaluating VOL-Async by the DKRZ (Deutsches Klimarechenzentrum GmbH Hamburg). Please consider me to be a novice HDF user. I’m … --- ## [VOL-REST: H5Fget\_filesize()](https://forum.hdfgroup.org/t/vol-rest-h5fget-filesize/11945)
**Author:** [@jan-willem.blokland](https://forum.hdfgroup.org/u/jan-willem.blokland)\ **Replies:** 3\ **Last updated:** [January 26, 2024, 10:35am UTC](https://forum.hdfgroup.org/t/vol-rest-h5fget-filesize/11945 "2024-01-26T10:35:16Z")
Hello, The other day, I got a request to implement functionality to retrieve the file size of HDF5 file via the library we have written on top of the HDF5 library. Fortunately, HDF5 library provides the function H5Fget\_… --- ## [ROS3: required version of cURL and OpenSSL](https://forum.hdfgroup.org/t/ros3-required-version-of-curl-and-openssl/11532)
**Author:** [@jan-willem.blokland](https://forum.hdfgroup.org/u/jan-willem.blokland)\ **Replies:** 2\ **Last updated:** [September 14, 2023, 9:14am UTC](https://forum.hdfgroup.org/t/ros3-required-version-of-curl-and-openssl/11532 "2023-09-14T09:14:58Z")
Hello, I have a small question. What is the minimum required version of cURL and OpenSSL to be able to make use of ROS3 VFD? If it is mentioned somewhere in the documentation, please point me to it. Otherwise it may be… --- ## [select\_construct\_projection in the VOL plugin](https://forum.hdfgroup.org/t/select-construct-projection-in-the-vol-plugin/11358)
**Author:** [@gesalous](https://forum.hdfgroup.org/u/gesalous)\ **Replies:** 2\ **Last updated:** [August 22, 2023, 5:38pm UTC](https://forum.hdfgroup.org/t/select-construct-projection-in-the-vol-plugin/11358 "2023-08-22T17:38:26Z")
Hello, I am developing a VOL plugin for Parallax LSM KV store (GitHub - CARV-ICS-FORTH/parallax: A persistent key-value store that is embeddable and optimized for fast storage.). In dataset write/read operations, the m… --- ## [VOL-REST: memory-side hyperslab unsupported?](https://forum.hdfgroup.org/t/vol-rest-memory-side-hyperslab-unsupported/11433)
**Author:** [@jan-willem.blokland](https://forum.hdfgroup.org/u/jan-willem.blokland)\ **Replies:** 3\ **Last updated:** [August 21, 2023, 8:57pm UTC](https://forum.hdfgroup.org/t/vol-rest-memory-side-hyperslab-unsupported/11433 "2023-08-21T20:57:45Z")
Hello, While using VOL-REST API, I have the impression that memory-side hyperslab is currently not supported. Is this true? When I use this memory hyperslab it writes the first part of the memory buffer instead of the s… --- ## [VOL-REST: H5is\_accessible() and H5Dset\_extent()](https://forum.hdfgroup.org/t/vol-rest-h5is-accessible-and-h5dset-extent/11375)
**Author:** [@jan-willem.blokland](https://forum.hdfgroup.org/u/jan-willem.blokland)\ **Replies:** 10\ **Last updated:** [August 21, 2023, 3:46pm UTC](https://forum.hdfgroup.org/t/vol-rest-h5is-accessible-and-h5dset-extent/11375 "2023-08-21T15:46:10Z")
Hello, Currently, we have written a library on top of the HDF5 library for store large models. Recently, we have implemented support for Read-Only S3 (ROS3) in this library by leveraging the ROS3 feature of HDF5 library… --- ## [memory backed files](https://forum.hdfgroup.org/t/memory-backed-files/9878)
**Author:** [@eduardo.camargo](https://forum.hdfgroup.org/u/eduardo.camargo)\ **Replies:** 28\ **Last updated:** [April 24, 2023, 10:47pm UTC](https://forum.hdfgroup.org/t/memory-backed-files/9878 "2023-04-24T22:47:12Z")
I am having trouble to set up an image into a memory backed file. I’d like to set up a memory file, copy some data into it and then extract the a file image which will be set in another memory backed file (this last step… --- ## [Passthrough-VOL: Getting Dataset Layout Information](https://forum.hdfgroup.org/t/passthrough-vol-getting-dataset-layout-information/10565)
**Author:** [@mtang11](https://forum.hdfgroup.org/u/mtang11)\ **Replies:** 3\ **Last updated:** [December 12, 2022, 6:22pm UTC](https://forum.hdfgroup.org/t/passthrough-vol-getting-dataset-layout-information/10565 "2022-12-12T18:22:26Z")
I am using a passthrough-VOL (short as pt-VOL below) to trace the HDF5 operation coming from a python program (using h5py). I am using HDF5 13.0.1 with h5py 3.7. The VOL I am using is very similar to the templates vol-ex… --- ## [VOL environment variables](https://forum.hdfgroup.org/t/vol-environment-variables/10416)
**Author:** [@wkliao](https://forum.hdfgroup.org/u/wkliao)\ **Replies:** 5\ **Last updated:** [November 9, 2022, 3:53am UTC](https://forum.hdfgroup.org/t/vol-environment-variables/10416 "2022-11-09T03:53:57Z")
A nice feature of VOL is by setting 2 environment variables HDF5\_VOL\_CONNECTOR and HDF5\_PLUGIN\_PATH, users can enable the VOL without changing their application source codes. While developing a new VOL, we found that HD… --- ## [VOL: Unable to Write a Dataset at File Close Time](https://forum.hdfgroup.org/t/vol-unable-to-write-a-dataset-at-file-close-time/10378)
**Author:** [@zanhua](https://forum.hdfgroup.org/u/zanhua)\ **Replies:** 1\ **Last updated:** [November 1, 2022, 4:58pm UTC](https://forum.hdfgroup.org/t/vol-unable-to-write-a-dataset-at-file-close-time/10378 "2022-11-01T16:58:31Z")
Hi there, Brief summary of the problem I am trying to develop a new VOL that is basically a Passthru VOL but does the following extra thing at file close time: create a new HDF5 dataset called TEST\_DSET (assuming no o… --- ## [Memory management in H5FD\_class\_t](https://forum.hdfgroup.org/t/memory-management-in-h5fd-class-t/9452)
**Author:** [@lucasvr](https://forum.hdfgroup.org/u/lucasvr)\ **Replies:** 12\ **Last updated:** [March 15, 2022, 10:00pm UTC](https://forum.hdfgroup.org/t/memory-management-in-h5fd-class-t/9452 "2022-03-15T22:00:49Z")
Hi, folks! The VFD interface provides a good abstraction for hardware-accelerated I/O routines. John Ravi’s GDS VFD is one such example: it uses NVIDIA’s GPUDirect Storage to initiate I/O to a cudaMalloc'd buffer provid… --- ## [Help Needed For Reading HDF5 files from AWS S3](https://forum.hdfgroup.org/t/help-needed-for-reading-hdf5-files-from-aws-s3/6800)
**Author:** [@mthirani](https://forum.hdfgroup.org/u/mthirani)\ **Replies:** 0\ **Last updated:** [March 13, 2020, 1:00pm UTC](https://forum.hdfgroup.org/t/help-needed-for-reading-hdf5-files-from-aws-s3/6800 "2020-03-13T13:00:17Z")
We are trying to read h5/ hdf5 files stored in S3 using the sample connector/ programs provided in https://www.hdfgroup.org/downloads/hdf5-enterprise-support/hdf5-connector-for-apache-spark/hdf-connector-for-apache-spark… --- ## [HDF5 ODBC connector status](https://forum.hdfgroup.org/t/hdf5-odbc-connector-status/6141)
**Author:** [@ken.walker](https://forum.hdfgroup.org/u/ken.walker)\ **Replies:** 6\ **Last updated:** [February 17, 2020, 3:39pm UTC](https://forum.hdfgroup.org/t/hdf5-odbc-connector-status/6141 "2020-02-17T15:39:37Z")
I found some old posts (ca 2015-17) about a HDF5 ODBC connector, but can’t find it on the download page. What’s the status? Is it no longer available? It appeared to be a promising start to read HDF5 data into Excel (wit… --- ## [HDF5 Connector for Apache Spark](https://forum.hdfgroup.org/t/hdf5-connector-for-apache-spark/6618)
**Author:** [@sulochana](https://forum.hdfgroup.org/u/sulochana)\ **Replies:** 0\ **Last updated:** [February 2, 2020, 1:44am UTC](https://forum.hdfgroup.org/t/hdf5-connector-for-apache-spark/6618 "2020-02-02T01:44:30Z")
Hi, I have a 2-TB of HDF5 files each 50GB to 500GB in size that are hosted on S3 bucket. I came to know that Spark Connector doesn’t work with S3. I don’t have enough hardware resources to copy this data locally. So, …