Synology 5bay Expansion Unit DX517 (Diskless) 157 mm x 248 mm x 233 mm

I've been using data storage products for decades professionally and at home. I used to build my own and eventually almost 10 years ago ended up with Synology. So far Synology has exceeded my (very high) expectations.A product should be judged on several metrics:1) product - the thing you buy2) Life cycle - the thing you buy over the period you have it3) support - can you get support when (not if) you have problemsFirst, Product.Synology DX1517: I added this DX1517 to my DS1517+ at my home office. I'll touch on overall Synology but focus on the DX1517 (this product).Synology storage products are centered around a Linux-based DSM, or Disk Station Manager that runs on their DS (Disk Station) line. For a home/small office environment, it's extremely powerful. DSM has very strong base functionality that is complimented by a long list of applications that you can add from both Synology and 3rd party vendors. Like Apps for your PC or phone, many of those applications are free. But like Microsoft Office with Windows, not all applications are free.One in particular that DSM requires payment for after a certain point is Surveillance Station. You can only run up to 2 cameras for free on Surveillance Station, after that you need to license Surveillance Station per camera (and despite what some incorrect reviews have stated) purchased camera licenses are transferable to other Synologies. I've done it.Further, if you can't find the application you want Synology also offers Docker so that you can add generic 3rd part apps if they are available in Docker containers. I have 10 apps installed that way and start/stop them as necessary. DSM and any installed application can work across any system volumes that DSM is aware of.Adding the DX1517 is simple: be sure everything is powered off, the disks are installed in the expansion unit, the eSata cable is inserted correctly and tightly screwed in on both ends, and then turn everything on. Magic, you have more disks. In DSM, create a new volume on the new expansion disks. It'll then do a consistency check the volume and then you're good to go. Done.So with this, I now have 50TB spread across the main and expansion unit in two volumes each in RAID 6. Yes, out of 10 disks I'm "wasting" 4. Read on.Here is the key: DO NOT SPREAD A VOLUME ACROSS eSATA CONNECTED DEVICES. I run a separate volume on the expansion unit (all, and I mean ALL, storage vendors strongly recommend that setup) so I have 2 volumes, one on the main DS unit, one on the DX unit. DSM doesn't care, and I certainly don't have a database or anything that needs more space than a single volume. Can you have only a single volume spanning devices? Sure you can. You can also drive most cars manufactured today over 100+ mph. But here's the difference: running a volume across an eSATA connection is like you ONLY being able to drive your car over 100mph ALL THE TIME. When (not if, but when) something goes wrong (which might be your own error, might not), the consequences sort of suck.RAID 6 only allows 2 disks redundancy. If I only had a single volume across my DS and DX and anything were to happen to either my DS, my DX, the power cords going to either, or the eSata cable connecting them, I'd lose 5 disks in the volume. So if I had one volume across both devices, that volume would lose 5 disks. 5 disk > 2 disks. RAID 6 isn't going to help much. Good luck. (For the purists, depending on the nature of the failure there is an outside chance that I could be able to re-establish read-only access to the volume if I can get all drives spinning again. But what would I rebuild 50TB onto ???)So TL;DR: the expansion unit just is and just works. It's transparent, and so long as it's installed correctly, I don't even think about it. I just interface with DSM.Second, Product Life-CycleSynology does an amazing job of keeping DSM and the core Synology Applications not only up to date for security and reliability issues but they actually increase functionality over time as you own your product. They don't just do that for the first year or while the product is under warranty - but so far for the DS+ series about 5 years or more after the product comes to market. This is a huge plus.Many companies put out a decent product then rush to develop another product they can sell and leave the previous products with old, buggy and insecure firmware. After awhile, what had been a decent product initially becomes incompatible, insecure, and effectively unsupportable (many lower-end phone vendors running Android do this - they simply don't offer updates when they're focused on their next product. Synology product life-cycle record has been first rate. Will it continue to be? Who knows, but the best indicator of future success is past success.Thirdly, Product Support.Storage device support is and should be centered around preventing data loss. I have first-hand experience with Synology live support on a DS1511+ I used to have. Superlative support: I had power problems in my house resulting in my DS being forced to restart repeatedly and ending up not being able to boot from disk. Contacted Synology support, within a day a human being actually manually logged into my system, un-messed it up, and I was good to go. Here's the kicker: the DS1511+ was out of warranty at the time, and they were aware of that. I was and still am impressed. Find another < $1,000 product that will do that. Then find one that will do that when the product is out of warranty. This kind of support is only even remotely feasible if the company keeps the products up to date - meaning, if the underlying product life-cycle is solid. Synology delivers here.I have to comment about the guy going all over Amazon screaming that they won't support the hardware product after the warranty period. First, Synology's base warranty is 3 years. Second, Synology offers extended warranties of 2 years if that's what you want, so you can get 5 years warranty. Finally, it's usually preferable and in the long run cheaper to replace a 3+ year old failed device than it is to get it fixed, particularly at these cost points. It depends what goes wrong: fans, PSUs are easily fixed by local talent. More than that, and even for a PC I'd recommend getting a replacement device. The old drives will work with the new device. If you're worried about Synology SHR RAID, just use RAID 6. Then you can go to any Linux-based device. But if you get a replacement Synology, just slot the drives in, boot it up and you'll be good to go.For a storage vendor, I'm happy if they prioritize data loss issues for real support. If I want help setting up Photo Station et al, there is a solid ecosystem in place for getting help both on the Synology web-site (forum, wiki) but also on other locations (reddit, SynoForum, etc).Overall, I still give Synology 5 stars.

TLDR: As an experienced user of data storage products, I'm impressed with Synology, particularly the DX1517 expansion unit. Its integration with the DS1517+ was seamless, offering robust functionality and reliable RAID 6 setup. The device's ease of setup and DSM's versatility stand out, though I advise against spanning a single volume across connected devices for safety reasons.Having spent decades both professionally and personally dealing with data storage, I've come to appreciate quality products. Synology, which I've been using for almost a decade, has consistently met and exceeded my high expectations.When evaluating a product, I consider three key metrics: the product itself, its lifecycle, and the support available. Focusing on the Synology DX1517, which I added to my DS1517+ at my home office, I'll discuss my experience with it, keeping in mind these criteria.First, the Product:The DX1517 expansion unit was straightforward to integrate with my existing DS1517+. Synology's products are based on the Linux-driven DSM, or Disk Station Manager, which I find to be extremely powerful for home/small office environments. DSM offers robust base functionality, enhanced by a wide range of applications from both Synology and third-party vendors. While many of these apps are free, some, like Surveillance Station, require payment after a certain point.I added the DX1517 easily. It required powering everything off, ensuring the disks were in the expansion unit, and securing the eSata cable. Once powered on, it was a simple process to create a new volume on the expansion disks in DSM.I now have 50TB across the main and expansion units in two separate volumes, each in RAID 6 configuration. It's crucial not to spread a single volume across eSATA-connected devices, as it risks the entire volume if there's an issue with one of the units or the connecting cable. In RAID 6, only two disks redundancy is allowed, so spreading a volume across both devices would risk significant data loss if more than two disks fail.Second, Life Cycle:From my experience, Synology products are durable and reliable over the long term. The DX1517 has proven to be no exception, continuing to function effectively without issues.Third, Support:Synology’s support has been adequate. While I haven't had significant issues requiring their assistance, it's comforting to know that help is available if needed.In conclusion, the Synology DX1517 is an excellent addition for anyone needing expanded storage. It's user-friendly, reliable, and integrates seamlessly with existing Synology systems. My advice to potential users is to be cautious with how you configure your volumes and understand the limitations of your RAID setup.