After working with Rockstor and weighing my options with HDDs, I've decided to go a slightly different direction...
I'm a big CentOS fan. I also have been wanting to learn more about Docker and BTRFS. This makes Rockstor with its "Rock-ons" and BTRFS filesystem the perfect choice. Or does it?
BTRFS seems to be Linux's answer to ZFS. However, it is not nearly as mature, feature complete or ready for primetime in my opinion. I wanted to work with 4+ drives which implies a RAID5/6 type of setup. I quickly found that BTRFS has some serious problems with its RAID5/6 implementation to the point where it corrupts data and therefore is not recommended for production. I could buy a true hardware-based RAID card for around $100, but I'm trying to avoid spending additional coin on this build (see Hardware section).
I'm "upgrading" from a Synology NAS. I love the simplicity and the 'it just works' factor it provides. Finding a NAS OS that provides a similar experience has proven to be difficult. Rockstor will not let you use any non-BTRFS filesystems on data drives. Per the RAID issue above and the fact that I did not get very good support from their somewhat inactive forums rules out Rockstor for this build. About the same time I started running into obstacles with Rockstor, I stumbled upon XPEnology.
While not officially supported by Synology, it is based on their OSS code and the forum appears fairly active. I've been testing it in a VM while waiting for some additional hardware parts to arrive (see hardware section). This is basically DSM on your hardware of choice. The real test will be the installation on the TS140-based system. This is in no way my final decision on the NAS OS as further testing is required.
The more I worked with the TS140's case, the less I liked it. Both internal drive trays require an L-shaped SATA connector since they're so close to the side of the case. Lenovo only provides one. That was the final straw. Luckily, I had a storage server case, an ARK 4U-500-CA that I was about to list on Craigslist but decided to use for this build. It fits nicely with my 'low cost, greater flexibility' theme. The rackmount hardware is removable. Just add some rubber feet on the bottom and presto-chango - it's a server tower case! It can hold at least 10 drives, has great air-flow and best of all - its free (to me).
In the next update, I'll detail the fun of moving the TS140 guts into a new case and some additional decisions required based on the number of drives needed.