Is it a good idea to use compressed NTFS filesystem on an external harddisk?

1) Yes, it is possible to access it from Liunx. As others explained, ntfs-3g is capable of handling compressed ntfs.

2) reliability: compression is in ntfs for a long time now (since Windows NT, see http://www.ntfs.com/ntfs-compressed.htm). I don't see any reliability problems on windows. I'm not that sure about non-windows implementations (e.g. linux). If your only concern is reading the data on linux, this is poses no reliability problem (mounting read-only is a good idea when restoring backups anyway).

Also data is compressed on cluster level which is usually 4 kiB. A physically corruption of the disk only affects single clusters, not entire files. In this regard compressed ntfs should be just as reliable as non-compressed.

3) Performance: The KB article you cite says performance might be affected on a server system, where the CPU is already saturated. On a desktop system with a current CPU as you describe it, using compressed ntfs for backups, should not have any significant performance impact. On the contrary, if you store compressible data, you might actually gain performance as you have less I/O. That is especially true, if the interface (USB 2.0) is slow compared to the CPU. I guess your CPU should easily be capable of saturating a USB 2.0 link writing or reading compressed ntfs.

4) If you set the compression flag for the entire filesystem you shouldn't have the problem of non-compressed moved files.

1. I think it is accessible from Linux, but I'm not sure.

2. Reliable in what sense? It's easier for your data to get corrupted, but I'm not sure if that's what you mean.

3. It's slower processor-wise, but faster I/O-wise. If your processor is much faster than your disk, then it might be worth it to read less data but do some processing, instead of reading huge files but avoiding postprocessing.

4. You can't avoid this, it depends on how the applications were programmed. I remember seeing a setting in Windows that had to do something with this, but I don't think it does what you need -- I'll update this if it turns out it does.

1. The ntfs-3g driver supports reading, appending and (recently) modifying compressed files.

   Currently reading compressed files is supported by all ntfs-3g versions. Creating new compressed files, clearing contents, and appending data to existing compressed files are supported since ntfs-3g-2009.11.14. Modifying existing compressed files by overwriting existing data (or existing holes) are supported since ntfs-3g-2010.8.8.

   — NTFS-3G Advanced: Data Compression

2. The filesystem is as reliable as its usual Linux counterparts, ext3/ext4.

   The ntfs-3g driver handles everything really well. (It might still have some bugs in modifying compressed files; as the above quote says, it has only been added in version 2010.8.8.)

3. (no answer)

4. When this is caused by programs creating an uncompressed file elsewhere and moving it to its intended location later, the workaround is easy: Re-enable compression on those files.