Part 3 – Finding a disk expansion module
A key element of our new NAS project is to find a disk expansion module with the following design requirements: linked via eSATA and using an internal SATA multiplier chip. We also have the following hopes for this unit: elegant, economical, minimal power consumption, silent, reliable, high performance.
In our scenario, this unit will take on the equivalent role of the Synology DX510 expansion unit which costs $500. At first glance, it seemed like a tall order unlikely to find as an off the shelf unit.
As luck would have it, a little research online shows that there are a number of such units available on the market. The main ones I could find at Newegg are from Rosewill and from SANS DIGITAL (TowerRAID).
The SANS DIGITAL units ship with a RR622 SATA III Controller card. Reviews show that it is unfortunately not very Linux friendly (a lot of griping and problems). Some user commented that he simply replaced it with another Linux friendly controller cart and the unit worked well. There is no hit of what SATA multiplier is used in those boxes. There are also reports/reviews saying that the fan is loud.
In contrast, the Rosewill family of SATA expansion boxes works GREAT! Reliable, economical, nice looking 100% Linux compatible. Their expansion boxes offer the same functionality as the DX510 AND are also based on the same Silicon Image SIL3726 port multiplier found in the Synology DX510, which should theoretically provide identical performance. The boxes come in 4, 5 or 8 disk expansion. They even bundle a good (i.e. reliable/ Linux compatible) PCIe 1x Sil3132 based host adapter.
- RSV-S4-X – 4 SATA 3.5″ disks, 150W PSU [$130 at NewEgg]
- RSV-S4-6G – identical to RSV-S4-X but ships with a RR622 adapter card (avoid!).
- RSV-S5 – 5 SATA 3.5″ disks, 220 PSU [$200 at NewEgg]
- RSV-S8 – 8 SATA 3.5″ disks 2 eSata connectors, 300W PSU [$300 at NewEgg]
I opted for the cheapest/smallest unig (RSV-S4-X) which works very well. In retrospect however, the two larger units come with actual disk caddies while the smaller unit requires you to use thumb screws to lock the disks in their respective trays. Not a big deal but the caddies are a nice professional touch. Given the chance to do it again, I would splurge the extra $70 and get the 5 disks unit with the caddies. This whole product family is cheap, reliable, fairly quiet and 100% compatible.
Choosing a eSATA controller card:
Most SATA cards are SATA-II (3Gb/s) links which can saturate most modern disks. With the advent of SSD disks, the SATA-III (6Gb/s) standard became necessary. For the purpose of our NAS box using regular mechanical disks, a SATA-II card will work just fine.
Any card based on the Sil3132 chip will provide 100% compatibility and reliability out of the box. Rosewill ships such a card with their disk expansion boxes. If for whatever reason, you need a different card, the following PCIe 1x cards should work nicely:
Note that the RR622 card is a 6Gb/s 2 port card. If you wanted to use a 6Gb/s capable 2 eSATA ports card, a little review of chipsets that are fully compatible with SATA port multiplier at ata.wiki.kernel.org shows that the Marvell 88SE9128/9125/9120/9111/9110 chips are fully compliants. A visit on the Marvell website identifies the 88SE9125 and possibly the 88SE9128 could be used as 6Gb/s SATA controler in a software RAID scenario and should be 100% Linux compatible right out of the box.
Having found the ideal disk expansion unit (cute, cheap, fast, reliable, 100% Linux compatible, and available in sizes 4/5 or 8), we can then focus on the main NAS box!