DX1215 Expansion Unit Performance Question

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DX1215 Expansion Unit Performance Question

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Long-time Synology user, here; but no hands-on experience with expansion units, so far. Here's the setup and question...

Assume two volumes (#1 & #2) on a DS3617xs, and another two volumes (#3 & #4) on an attached DX1215 - all four volumes use identical HDDs, RAID level, etc.

As I understand it, a copy from volume #1 on the DiskStation to volume #3 on the Expansion would be limited to around 6Gb/s max - essentially the same speed as a single SATA III drive - with no performance benefit from a multi-disk RAID. Correct?

My question is... Would a copy from volume #3 to volume #4 (both on the Expansion) run as fast as a copy from volume #1 to volume #2 (both on the DiskStation)?

Thanks.
 

Rusty

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My question is... Would a copy from volume #3 to volume #4 (both on the Expansion) run as fast as a copy from volume #1 to volume #2 (both on the DiskStation)?
It will, yes
 

jeyare

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As I understand it, a copy from volume #1 on the DiskStation to volume #3 on the Expansion would be limited to around 6Gb/s max - essentially the same speed as a single SATA III drive - with no performance benefit from a multi-disk RAID. Correct?

My question is... Would a copy from volume #3 to volume #4 (both on the Expansion) run as fast as a copy from volume #1 to volume #2 (both on the DiskStation)?
1. YES, copy between two volumes (main to/from expansion unit) is limited by single SATA III interface, then you are right
2. Follow Synology Expansion units solution guide (only for 1217, but there must be similar point of view), there is a difference between performance of main unit speed vs expansion unit (same SATAdisk in same RAID, sequential throughput). Better for the main unit up to 12,9% for write and 22,2% for read.
 

fredbert

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Better for the main unit up to 12,9% for write and 22,2% for read.
I wonder why that would be: because the hardware controller is in the main unit and the eSATA connection is shared with all the expansion unit's disks?
 

jeyare

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Yes. Problem is based on no dedicated controller. As you can see from the test cases.
 
83
35
NAS
2x DS1621xs+, DS220+
Router
  1. RT2600ac
  2. MR2200ac
Operating system
  1. macOS
Mobile operating system
  1. iOS
Thanks @jeyare for the link to Synology's Expansion Unit Guide; and to all for the discussion. This is very useful information for planning purposes. We have occasion to copy about 30TB at least a couple times per year. On a 1G or even 10G network with two DS1819+, it was intolerably slow (1 week or 3-4 days respectively). Whereas a copy between volumes on the same DS3617xs will run in just under 20 hours. R
 

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