Hello All, I am the one who was making a fuss about the yt ART frontend a few weeks ago. I think I have found the root of the problems I was having. I have a fork here with my changes, outlined below. https://github.com/sflarkin/yt The first change is a simple change from / to // to make a num_pages int check not fail. https://github.com/yt-project/yt/commit/f233658b153e0ee7b31b31f121488a4257cf... The second is the more important one. It appears that in the ART data structures file _find_files function, there were two check to find matching datafiles. One compared both the extension number and data file type, and found the correct file. The other second check just compared the data file type, meaning it found all files with the correct extension, like .DAT. This second check would then just dump the last one, which was incorrect. By removing the check, it appears to have fixed the problem, as shown by my run log below. P001 yt : [INFO ] 2018-08-06 14:44:40,241 discovered particle_header:/nobackupp2/sflarkin/VELA07test/PMcrda0.051.DAT P001 yt : [INFO ] 2018-08-06 14:44:40,241 discovered particle_data:/nobackupp2/sflarkin/VELA07test/PMcrs0a0.051.DAT P001 yt : [INFO ] 2018-08-06 14:44:40,242 discovered particle_stars:/nobackupp2/sflarkin/VELA07test/stars_a0.051.dat P001 yt : [INFO ] 2018-08-06 14:44:40,263 Using root level of 14 P001 yt : [INFO ] 2018-08-06 14:44:40,265 Discovered 7 species of particles P001 yt : [INFO ] 2018-08-06 14:44:40,265 Particle populations: 34930688 4943872 855040 139392 21776 2088309 2 P001 yt : [INFO ] 2018-08-06 14:44:40,483 Max level is 08 P001 yt : [INFO ] 2018-08-06 14:44:40,495 Parameters: current_time = 0.2068722930617056 Gyr P001 yt : [INFO ] 2018-08-06 14:44:40,496 Parameters: domain_dimensions = [128 128 128] P001 yt : [INFO ] 2018-08-06 14:44:40,496 Parameters: domain_left_edge = [0. 0. 0.] P001 yt : [INFO ] 2018-08-06 14:44:40,496 Parameters: domain_right_edge = [1. 1. 1.] P001 yt : [INFO ] 2018-08-06 14:44:40,496 Parameters: cosmological_simulation = True P001 yt : [INFO ] 2018-08-06 14:44:40,496 Parameters: current_redshift = 18.578137813635497 P001 yt : [INFO ] 2018-08-06 14:44:40,496 Parameters: omega_lambda = 0.7300000190734863 P001 yt : [INFO ] 2018-08-06 14:44:40,496 Parameters: omega_matter = 0.27000001072883606 P001 yt : [INFO ] 2018-08-06 14:44:40,496 Parameters: hubble_constant = 0.699999988079071 [ 141s] Sending projection requests... [ 143s] Transferring particles to writers... [ 146s] Analyzing for FoF groups... [ 148s] Transferring boundary particles between writers... [ 148s] Linking boundary particles... [ 149s] Analyzing for halos / subhalos... [ 150s] Loading merger tree information... [ 151s] Constructing merger tree... [ 152s] [Success] Done with snapshot 3. [ 152s] Reading 1 blocks for snapshot 4... P001 yt : [INFO ] 2018-08-06 14:45:21,705 discovered particle_header:/nobackupp2/sflarkin/VELA07test/PMcrda0.060.DAT P001 yt : [INFO ] 2018-08-06 14:45:21,705 discovered particle_data:/nobackupp2/sflarkin/VELA07test/PMcrs0a0.060.DAT P001 yt : [INFO ] 2018-08-06 14:45:21,705 discovered particle_stars:/nobackupp2/sflarkin/VELA07test/stars_a0.060.dat P001 yt : [INFO ] 2018-08-06 14:45:21,728 Using root level of 14 P001 yt : [INFO ] 2018-08-06 14:45:21,755 Discovered 7 species of particles P001 yt : [INFO ] 2018-08-06 14:45:21,755 Particle populations: 34930688 4943872 855040 139392 21776 2088309 149 P001 yt : [INFO ] 2018-08-06 14:45:21,948 Max level is 09 P001 yt : [INFO ] 2018-08-06 14:45:21,961 Parameters: current_time = 0.2648085269122017 Gyr P001 yt : [INFO ] 2018-08-06 14:45:21,961 Parameters: domain_dimensions = [128 128 128] P001 yt : [INFO ] 2018-08-06 14:45:21,961 Parameters: domain_left_edge = [0. 0. 0.] P001 yt : [INFO ] 2018-08-06 14:45:21,961 Parameters: domain_right_edge = [1. 1. 1.] P001 yt : [INFO ] 2018-08-06 14:45:21,961 Parameters: cosmological_simulation = True P001 yt : [INFO ] 2018-08-06 14:45:21,961 Parameters: current_redshift = 15.606548426007368 P001 yt : [INFO ] 2018-08-06 14:45:21,961 Parameters: omega_lambda = 0.7300000190734863 P001 yt : [INFO ] 2018-08-06 14:45:21,962 Parameters: omega_matter = 0.27000001072883606 P001 yt : [INFO ] 2018-08-06 14:45:21,962 Parameters: hubble_constant = 0.699999988079071 As can be seen, this shows that two grids were loaded with the correct files. I am not sure if there is some edge case that the second check was meant to catch, as I cannot think of any. Are there any I am not aware of?