For a long time, Strato customers were quite limited when it came to creating files using scripts. In principle, Strato customers could not use any backup plugin for WordPress. Because Strato limited the files that a script could create itself to 64MB.
Mind you, of course you could upload larger files via FTP. But if a PHP script wanted to create a file, it could be a maximum of 64MB in size. Since the vast majority of websites are larger these days, all backup attempts have failed.
But before you get the wrong impression here: this limit has been lifted. In September I asked Strato via Twitter:
Hey @STRATO_AG! WordPress backups fail with you because of the 64MB file size limit for PHP scripts. I only know about you. What to do?
— Marc Nilius (@marcnilius) September 22, 2016
The answer was (among other things) a link to the info that Strato has increased the PHP memory limit and file upload limit. A test showed that the said file size limitation no longer existed, even if the changes described in the blog were not causally related to it.
@SniperSister @marcnilius Cast: https://t.co/9Cqb9rhCMA
— STRATO AG (@STRATO_AG) September 22, 2016
But at some point there was also a statement:
@marcnilius @SniperSister I checked again. The max write file under PHP 7 is 1024 MB.
— STRATO Hilt (@STRATO_hilft) September 27, 2016
So there is still a size limit for files that are created using a script. However, 1024MB makes much more sense than 64MB. Many backups can simply go through with it without any problems. Only in rare cases does this limit slow you down.
Incidentally, I could not discover any connection to the PHP version (as well as mentioned in the tweet).