I use DOS 6 with QEMM 7 and have no problems, even WITH compression!
DoubleSpace is quite reliable so long as you follow common sense, such as:
* Always do a "SMARTDRV /C" before powering off or rebooting. To date,
most cases of corrupted DoubleSpace volumes have been traced to the
cache not being flushed. If you think you might not be able to enforce
this, disable write-back caching entirely by specifying the drive letter
with no "+" nor "-" in the SMARTDRV line in your AUTOEXEC.BAT. (The DOS
6.2 version of SMARTDRV will default to write-back cache off, and you
will have to specify the drive letters with a plus sign if you want the
write caching enabled — it DOES speed things up considerably, at the
cost of reliability if you should fail to flush the cache.)
* Keep an uncompressed volume for such things as Windows and Phar Lap
(3DS) swap files.
* Don't use old versions of utilities such as Norton or PC-Tools on
DoubleSpaced volumes. Use only utilities which are certified to work
with DoubleSpace, such as PC-Tools version 8 or later.