2 x 1GbE Links But Only 1GbE Writes

[Robbie]

I'm scratching my head on this one as since my last actual test we have had DSM updates, macOS updates and probably a switch update.

The NAS is my RS217, so weak in just about every area, running with 2 x 1GbE links (it only has 2 ethernet ports), no LAG, no Bond, large MTU, SMB3. Volume is a single SSD and no errors or issues reported anywhere. I noticed that it seemed to be running slower on transfers so ran a few tests and double-checked network settings.

For read speed I am getting around 230MB/s (slightly up on last year) but only peaking at around 130MB/s and typically around 115MB/s for writes - close to 1GbE speed. It used to be around 200MB/s for writes and no lower than 180MB/s. Data throughput is being shared equally between the 2 x 1GbE links.

As an example using a typical speedtest app:

DSM7 Resources - not exhausting the (anaemic) CPU or RAM:

DSM7 Settings:

My switch port settings (port 17&18 being used for this NAS):

NAS SMB config:

root@Dragon:~# cat /etc/samba/smb.conf
# Copyright (c) 2000-2019 Synology Inc. All rights reserved.
## Don't Panic, in big friendly letters ##

[global]
    server multi channel support = yes
    aio read size = 0
    aio write size = 0
    printcap name=cups
    winbind enum groups=yes
    include=/var/tmp/nginx/smb.netbios.aliases.conf
    encrypt passwords=yes
    min protocol=SMB2_10
    security=user
    local master=no
    realm=*
    syno sync dctime=no
    passdb backend=smbpasswd
    printing=cups
    max protocol=SMB3
    winbind enum users=yes
    load printers=yes
    workgroup=WORKGROUP
root@Dragon:~#

Can anybody clue me in as to why the link only achieves around 1GbE speeds for writes or spot an error anywhere?

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[Coop777]

this is by design and a limit of 1 GBE. You will need to upgrade to 10 GBE for faster write speeds.

 

[Robbie]

@Coop777 Thanks but your answer makes no sense at all, at least on its own.

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[AdrianEarnshaw]

When you say used to be, was that before dsm7? It looks like you are saturating the gb network speed, so not sure what you are looking for here.

 

[Robbie]

Amongst other things yes, previous tests were under DSM6 but reasonably sure I tested it under DSM7 beta but didn't keep a record so I guess it was unremarkable.

There is 2Gbps of bandwidth available (less overheads) and I am achieving that in one direction - 231MB/s or 1.85Gbps in the example above - but only 131MB/s or 1.048Gbps in the other direction.

I'm wondering about the CPU again as if I lower the MTU to 1500 the write speed drops to 90MB/s, suggesting that it is a packet limitation.

 

[AdrianEarnshaw]

The data sheet for the RS217 suggests maximum write speed of 127.51mb/s so I cannot see anything wrong with the stats you posted.

 

[Robbie]

@AdrianEarnshaw - Thanks and it looks like you are on to something as the online data sheet does say that... now.

It used to say 171.7MB/s, which is around what I could get with spinners whilst achieving the figures in the first post with SSDs. I wonder what Synology did that reduced the maximum write speed by such an amount.

The original datasheet:

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[AdrianEarnshaw]

Sorry I haven’t a clue why. Maybe extra overheads from DSM7 on a 2 - 3 year old product??

 

[Robbie]

Could be, as they left the RS217 kernel unchanged (and rather old) with the move to DSM7.

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[Robbie]

DSM7.1 will probably flush-out issues such as this as it will bring multichannel link aggregation to a wider base of users.

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