Back to USB3 transfer speed (lost in description):
- USB3 is just the name of 3rd major version for Universal Serial Bus standard
- the USB3 standard has definition of max. speed = 5Gbps (625MBps), this is just theoretical speed of bus, not a real speed of device connected to the bus
- there is also USB3.1 ver (called also USB-C) with possible 10Gbps (1250MBps)
Then there are main bottleneck definitions for the real USB3 data transfer speed:
a) performance limitations of device where you have data stored
b) performance limitations of device where you would like to data move in
c) adapters/converters/disk controllers between a) & b), like SATA to USB, etc. ... try to find identical environment
Independent disk controller can provide better performance as basic (frequently low cost, part of main board) utilized by CPU only. But some vendors can surprise me (positively). One of the reason, why a small factor board in the NAS is worse than PC (in case of USB3 transfer).
The disk performance is another point. I will provide sample of mentioned Western Digital Blue range disks here. There is no "normal" disk, just clearly defined.
Example no 1:
WD Blue 5400rpm 160GB HDD with SATA II 8MB buffer with avg 360Mbps (45MBps) for sequentilal large files W/R (write/read)
but same HDD with random speed test of 4k blocks can provide only avg 7Mbps (0.84MBps) W/R
... pretty far from 3Gbps SATA II theoretical speed
Example no 2:
Same WD Blue 250GB HDD, but: with 7200rpm with SATA III 16MB buffer
will provide
avg 664Mbps (83MBps) for sequentilal large files W/R
avg 9Mbps (1.06MBps) random speed test of 4k blocks W/R
... pretty far from 6Gbps SATA III theoretical speed
Example no 3:
rocket star of WD the Gold 1TB HDD, with 7200rpm with SATA III 128MB buffer
will provide
avg 1200Mbps (150MBps) for sequentilal large files W/R
avg 22.72Mbps (2,84MBps) random speed test of 4k blocks W/R
... still pretty far from 6Gbps SATA III theoretical speed
Example no 4:
Samsung 840EVO 256GB SSD, with SATA III 3 GB Turbowrite cache
will provide
avg 2784Mbps (348MBps) for sequentilal large files W/R
avg 450Mbps (56.2MBps) random speed test of 4k blocks W/R
... better, but still pretty far from 6Gbps SATA III theoretical speed
As you can see, there is most important point - chosen block structure (except SATA bus):
- small block (4096 B) will save your usable data space, but will make a heavy pressure to your disk performance
- bigger block (256kB - 4MB) will up side down this problem ... common SSD block size, e.g. Samsung SSD 840 EVO has blocks of size 2048 KB
This is the reason, why two "similar" benchmarks approach will be always different on identical disk (but different format).
Then there is no "normal" disk definition. You still need to think about the exact purpose:
- low cost, but pretty slow disk
- costly, but without a guarantee of the performance (the block setup can slow down the performance)
- midway between the cost and usable data space (chosen block size) and final performance
Then if you put faster HDD/SDD to "USB3" box it will provide just small portion of USB3 potential.
Yes, of course there is a question who will put such slow disk to USB3 box. Many of vendors/users
.
Finaly:
still if you have strong performed SSD with SATA III and 4MB block size in your USB3 box (wit super trouper adapter from SATA II to USB3 in the box) your performance in the NAS will be slow. Why?
Because all of the Syno NAS under RS/XS range are assigned to Retail and really SME. I think, that USB3 performance is not a main driver of Synology evolution. And the USB3 is not main connection side of the NAS (network attached storage).
But this is not an apology of Synology side. Just my point.
Valid for SD card also.
And another point is used File system.
You can find some statistics
here. If they are useful? I don't know, because there is still main point - your approach to many of mentioned bottlenecks.
