External Hard disk must conform to eSATA, FAT32.
Q1. Is there a limit on the eSATA external HDD on the DL850?
A1. The maximum size is 1.5 TB.
Q2. What is data saving rate for internal HDD?
Q3. What is data saving rate for external HDD?
A2&3. Actual rate is 3.2MB/s. I believe all of HDD with eSATA-IF can be used.
The external HDD recording function is same performance with internal one.
The maximum compatible eSATA external HDD size is 1.5 TB. The external HDD recording function performs the same as the internal HDD. The actual data transfer for internal and external HDD is 3.2 MB/s.
One limitation is that the DL850E/EV is not the best way to format the HDD (the process may never complete), please use one of these utilities instead, Verbatim and Rufus:
http://www.verbatim.com/index/search.php?words=fat32+tool
https://rufus.ie/en/
Windows may or may not do it reliably either. The Verbatim tool is the very best way, and very fast, and Rufus has been shown to work well also.
Some more ideas:
Do not hot-swap the HDD … from the DL850, it is not supported;
Buy a spare eSATA cable, they do wear out:
https://www.amazon.com/StarTech-6-Feet-Shielded-External-ESATA6/dp/B000ENYXZ6/ref=pd_bxgy_147_2?_encoding=UTF8&psc=1&refRID=F25GCXT7ACQ95A2YJ9X2
Buy a eSATA HDD that also has a USB port … it will come in handy on your PC to move data over; ideally USB3.0 if you can find it;
Recommended drive:
Andy tested the FANTOM a few years back and it is great, but partition it as 1.5TB and as 0.5TB or just buy two 1TB versions of it; ANY eSATA drive will work, just be sure to use the VERBATIM tool on it – that is very important – windows may not properly format it;