DSM 7.0 DX517 separate volume necessary?

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DSM 7.0 DX517 separate volume necessary?

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Hi - I have a DS1621+ for about a year now, and need to expand my space so I now have a DX517 on the way. I read in some places that it’s best to use DX517 as its own separate Volume, and not to expand from Volume 1 on main unit. Is this really what most people do and recommend? I can do this, but just curious what others do and why. I mainly use the NAS as a Plex server, and wondering about pros/cons of just keeping Volume 1 (by expanding it with DX517) vs. expanding it into a Volume 2 with additional Plex libraries on it. Thanks in advance for any feedback!
curious what others do and why
It's a math probability issue. Whether SHR or SHR2, when the communication breaks between those units, four drives disappear from the pool, forcing an unrecoverable crash. If that's a risk you are good to take, then there is no issue.

For the cost of a DX, it may be worth considering a second NAS... or using 18 TB drives on the DS.
Send it back and do as I was advised - buy another NAS.

Way-more secure, flexible and a much better buy. Expansion units would have to be very cheap to be worth it over a proper NAS and, well, they just aren't.

Two NASes are better than one!

Thanks for the feedback! My Drobo 5Dt broke down again recently and the 5 year warranty expires next month. I just got the replacement Drobo unit this week and been thinking about how to replace it as I don’t want to go thru using a Drobo again for various reasons (used as my primary Plex server). So my thought was to get the DX517 as my “Drobo replacement“ and just have it all on the NAS network (though I do like having a DAS for speed … I wish Synology made one). Been pretty happy with Plex on the Synology though for my secondary libraries (I have Plex both on Drobo DAS and Synology NAS), and the side benefit of Synology is that it doesn’t require my Mac to be on all the time in order to use Plex (very handy for when I’m not at home when problems happen).

I struggle trying to keep backups with such large amounts of data though that just keeps growing… which is a different topic I know. I’m just utilizing multiple large external harddrives for this.

I think I’ll keep the DX517 (I got it at a good price) and make it ‘Volume 2’ to migrate my Drobo Plex libraries onto it, while maintaining my existing libraries on the DS (just to keep my maintenance, organization and sanity as slim as possible :) Good to know about what happens to my drives if there is a communication breakdown, so I will keep it as its own volume then!

Since I still feel like a complete newbie to Synology and NAS in general, this makes me more comfortable. But I certainly want to learn and am open to hearing what other folks do to help with this journey… Thanks again for the input!
@timmo - You mentioned speed as a priority in your last post and unfortunately this is another strike against an expansion box and it is all down to that little single cable again.

For whatever reason these NASes use SATA backplanes so you get SATA drives and the eSATA link to the expansion box. SATA is a bit rubbish at the best of times as it is only half-duplex - it can only send or receive data rather than transport both at the same time, effectively halving throughput.

The main NAS box will (to some degree) lighten the burden of this potential bottleneck by having a SATA interface with each drive and aggregating the bandwidth and I/O of each of your 6 SATA drives together across a SATA backplane that can handle multiple SATA interfaces - hurrah!

Instinctively you know this all anyway so think about it from the point of the 5-bay expansion box. Five drives all wanting mixed read/writes sharing a single SATA backplane and a single SATA connection to the main NAS that only moves data one way at a time.

This cluster 'f' of data now has to be managed by the CPU and RAM of the main unit as it tries to juggle this single ugly stepchild of SATA on its backplane that has 5 drives hanging off it rather than the 1 it would rather have. At best you get a 5th of the performance that you would like but in reality it never gets this good as the inter-drive traffic holding the RAID parity together is fighting for the same limited resource.

Even as a distinct volume the clucking expansion box will still drag down the resources of the main unit and if you did something mad like span a volume over the link then the whole assembly would run at the slowest rate governed by that single one-way-at-a-time-sweet-***** eSATA link.

[pst... sell it, buy a proper NAS]
now has to be managed by the CPU and RAM of the main unit as it tries to juggle this single ugly stepchild of SATA on its backplane that has 5 drives hanging off it rather than the 1 it would rather have
@Robbie 's post is the best summary I've run across.

Additionally, since the OS and swap partitions are mirrored across all drives, even hardware separated pools performance suffer due to the half-duplex communication between the DS and DX.
@Robbie thanks for making me laugh out loud. Very good/interesting info … I wish I learned this when looking at reviews of the DX517 (unless I just didn’t read the right articles) … I thought I researched it pretty well. Sigh … not sure what to do now. I just need it for Plex expansion and trying to keep it simple if I can (I don’t think I’m ready yet for multiple NAS units … yet :)

Let’s pretend that I do keep it and I set it up as either JBOD or SHR for this new Volume2 on it (curious if it matters much between JBOD vs SHR with regards to Plex performance?). Also curious as I manage all my media on my Mac first before transferring it to the NAS, if the transfer speeds to the DX517 would be significantly less than transferring data to the DS (maybe half the speed if that’s what it means when you mention half-duplex)? That’s what I like about Drobo DAS - fast speeds in managing everything with the media. I have quite a speed drop when transferring to the NAS libraries (and I’m directly connected via ethernet from Mac to Router to NAS). So my workflow will slowdown some in having all my Plex libraries on the NAS/expansion unit, but am willing to take that hit to have it running on its own server. At most there are 2-3 streams running at one time on the Drobo libraries (and that’s rare), and I only stream 4k locally (with the 4k libraries hosted on the NAS) as it never seems to work to remote stream 4k outside the home network when that media is on either the Drobo or NAS (I believe this is a known limitation … not sure if/when that will ever change for most people).

Then this makes me question the media Types to host on DS vs DX for maximum performance / less problems in streaming (if that would come up) - e.g. is 4k better on DS or maybe offload it to the DX since that is streamed locally?

Sorry for all the questions … and I know it gets away from the recommendation of buying a new NAS instead :) I really do appreciate any input/advice, so thanks for entertaining this as much as you can stomach :)
I'm not best placed to advise on how to handle data with an expansion unit.

I like to helpful though, so I'll be ready with a tissue when the tears come. 😱

My ugly stepchild is now setup and connected :) After its done doing its thing, I'll start moving data onto it and see if I made a really bad decision here ...

So far so good on the DX ... I am getting the same read/write speed to it over the network as the DS. This is promising:

Let go of your 1GbE... search your feelings, you know 10GbE is true...
I have always wondered why I can’t get any faster speeds to the DS. My mac is connected via Ethernet which goes direct to my newish netgear switch (S350) which then connects directly to the NAS. Looking at my switch I now see that it is gigabit (maybe I should have bought a 10gb switch?). Even if its 1GbE, I’m confused as to why my speed would be ~105mb to/from the NAS. I am only using 1 of the 4 Ethernet ports on the NAS because I haven’t learned yet how to utilize the other ports if it can increase the speed with what I have.
105MB/s = about maximum real life speed for a 1Gbps Ethernet (difference MByte/s vs mbit/s is factor 8)!
No need for a 10GBe switch, unless all nic's and cables support it.

Your other ports on the nas will typically not increase speed to a single mac.

10GbE is very nice to have. Using multiple ethernet ports to increase throughput to a single client is not (fully) supported yet but should arrive with DSM7.1.

Wow - that would save me some serious time shuffling files around from mac to NAS
I'm in a similar situation as @timmo as I have a couple of Drobos that I'm working on migrating to my syno. I initially thought I would use the Drobos as an added backup but have realized, I don't like that I can't send snapshots to them (or at least haven't figured out how to get them formatted to btrfs via Linux without using some kind of nested VM with a nested network share). Even if I could, I'm guessing I still need to have it connected to something like my Mac Mini.

I also have considered the expansion unit approach after looking at other plus (+) series NAS units—or whatever is minimal that can utilize btrfs.

I understand all of the eSATA and "dumb" box limitations mentioned in this thread.
My question is... what is perhaps an ideal use case for an expansion unit?

Im hoping to simply take 5 drives and throw them in a box that wakes up for a few minutes once a day and sends btrfs snapshots to it and then goes back to sleep. I realize I can do this with another NAS but even if it's using minimal power, surely it's still burning a bit more juice sitting idle than a DX with all drives spun down.
My secondary NAS is only timed to come on for receiving the Hyper Backup from the prime. Outside of that it is effectively 'off' with only the tiny quiescent power draw to enable the switch-on from either the front panel button or via the timed schedule.

The net effect is that it is only on for about 1hr30min x 3/7 = 4.5hrs a week. The small variance in actual backup times achieved is more significant in terms of power than the quiescent power used in the other 163hrs+ a week in its 'off' or 'shutdown' state.

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