As you saw in the previous section, the file content is not yet retrieved on the file system. However, nothing prevents you from accessing your files as you would on any other POSIX compliant file system. When accessing the file, the actual content is retrieved. The file access latency is slightly higher for the first access, but once the content has been retrieved, file access latency drops to a sub-millisecond latency because it is served by the file system on subsequent accesses. In addition, releasing a file from the file system does not delete the file but removes its actual content. The metadata is still be stored on the file system.
In this section, you learn more about the lazy loading functionality, observe the performances between consecutive accesses, then learn about file content removal.
First, use command lfs hsm_state /shared/SEG_C3NA_Velocity.sgy to check that the file data is not loaded on Lustre:
lfs hsm_state /shared/SEG_C3NA_Velocity.sgy
/shared/SEG_C3NA_Velocity.sgy: (0x0000000d) released exists archived, archive_id:1
You should see that the file is released exists archived.
Now, check the size of the file with ls -lh /shared/SEG_C3NA_Velocity.sgy:
ls -lh /shared/SEG_C3NA_Velocity.sgy
-rwxr-xr-x 1 root root 455M Jun 22 23:26 /shared/SEG_C3NA_Velocity.sgy
As shown above, the file size is about 455 MB.
For this step, you read the file and measure the time it takes to load it from the linked Amazon S3 bucket using the HSM. You write the file to tempfs.
Use the following command to retrieve the file:
time cat /shared/SEG_C3NA_Velocity.sgy > /dev/shm/fsx
real 0m6.701s
user 0m0.000s
sys 0m0.294s
It took about 6 seconds to retrieve the file. The data was copied from S3 to the FSx for Lustre file system and to the head node.
Run the command again and see the access time:
time cat /shared/SEG_C3NA_Velocity.sgy > /dev/shm/fsx
real 0m0.169s
user 0m0.000s
sys 0m0.168s
This time it took only .17 seconds.
The new access time is a bit too fast because the data has been cached in memory on the head node instance. Now, drop the local caches on the head node and repeat the command again.
sudo bash -c 'echo 3 > /proc/sys/vm/drop_caches'
time cat /shared/SEG_C3NA_Velocity.sgy > /dev/shm/fsx
This access time is more realistic:
real 0m0.591s
user 0m0.005s
sys 0m0.312s
This file was retrieved from FSx for Lustre without caching on the head node and without copying from S3.
Next, look at the file content state through the HSM.
Run the command lfs hsm_state /shared/SEG_C3NA_Velocity.sgy:
lfs hsm_state /shared/SEG_C3NA_Velocity.sgy
/shared/SEG_C3NA_Velocity.sgy: (0x00000009) exists archived, archive_id:1
You can see that the file state changed from released exists archived to exists archived.
Now, use the following command to see how much data is stored on the Lustre partition.
lfs df -h
UUID bytes Used Available Use% Mounted on
unnznbmv-MDT0000_UUID 34.4G 9.2M 34.4G 0% /shared[MDT:0]
unnznbmv-OST0000_UUID 1.1T 471.5M 1.1T 0% /shared[OST:0]
filesystem_summary: 1.1T 471.5M 1.1T 0% /shared
Do you notice a difference compared to the previous execution of this command? Instead of 7.5 MB of data stored, you now have 471.5 MB. In this case, it is stored on the second OST, your may see slightly different results.
In this step, you release the file content. This action does not not delete nor remove the file itself. The metadata is still stored on the MDT.
Use the following command to release the file content:
sudo lfs hsm_release /shared/SEG_C3NA_Velocity.sgy
Then, run this command to see again how much data is stored on your file system.
lfs df -h
UUID bytes Used Available Use% Mounted on
unnznbmv-MDT0000_UUID 34.4G 9.2M 34.4G 0% /shared[MDT:0]
unnznbmv-OST0000_UUID 1.1T 7.5M 1.1T 0% /shared[OST:0]
filesystem_summary: 1.1T 7.5M 1.1T 0% /shared
You are back to 7.5 MB of stored data.
Access the file again and check how much time it takes. It should take around 6 seconds. Subsequent reads use the client cache. You can drop the caches, if desired.
time cat /shared/SEG_C3NA_Velocity.sgy >/dev/shm/fsx
real 0m5.819s
user 0m0.000s
sys 0m0.327s
time cat /shared/SEG_C3NA_Velocity.sgy >/dev/shm/fsx
real 0m0.203s
user 0m0.000s
sys 0m0.202s
sudo bash -c 'echo 3 > /proc/sys/vm/drop_caches'
time cat /shared/SEG_C3NA_Velocity.sgy >/dev/shm/fsx
real 0m0.618s
user 0m0.000s
sys 0m0.351s
In the next step, you install IOR, an IO parallel benchmark tool used to complete performance tests on your Lustre partition.