You are absolutely correct. The difference is exactly due to the TRIM command and is directly related to HBS's current lack of support for the EXT4 filesystem.
On the SSD: TRIM causes the SSD to return zeros for all unused blocks. Because HBS performs a full sector-by-sector backup (as it cannot interpret EXT4 to skip empty space), it reads these zeros, which compress perfectly. This results in a small backup file.
On the Mechanical HDD: HDDs do not support TRIM. The unused space is filled with old, random data. Since HBS cannot filter this out for EXT4, it must back up this data with low compression rates, resulting in a large image file nearly the size of the entire partition.
Therefore, the issue is a combination of two factors:
1. HBS does not support the EXT4 filesystem, forcing it to back up the entire partition at the sector-by-sector mode.
2. The storage hardware's handling of unused space (SSD with TRIM vs. HDD without) dramatically affects how well that sector-level backup can be compressed.
We apologize for any inconvenience caused by the lack of EXT4 support in the current HBS version. Your observation perfectly illustrates why this limitation leads to such different results on SSDs and HDDs.
On the SSD: TRIM causes the SSD to return zeros for all unused blocks. Because HBS performs a full sector-by-sector backup (as it cannot interpret EXT4 to skip empty space), it reads these zeros, which compress perfectly. This results in a small backup file.
On the Mechanical HDD: HDDs do not support TRIM. The unused space is filled with old, random data. Since HBS cannot filter this out for EXT4, it must back up this data with low compression rates, resulting in a large image file nearly the size of the entire partition.
Therefore, the issue is a combination of two factors:
1. HBS does not support the EXT4 filesystem, forcing it to back up the entire partition at the sector-by-sector mode.
2. The storage hardware's handling of unused space (SSD with TRIM vs. HDD without) dramatically affects how well that sector-level backup can be compressed.
We apologize for any inconvenience caused by the lack of EXT4 support in the current HBS version. Your observation perfectly illustrates why this limitation leads to such different results on SSDs and HDDs.