Gigabit LAN, why is write much slower than read?

[rtilghman]

Recently finished install on a home 802.11n / gigabit network. I've been testing the network post install with LAN Speed Test, and I'm encountering a couple of issues.

1. The Synology read/write speeds are half what I can get to other devices (which I'm assuming is partly the WD green 5400 RPM drives),
2. No matter WHAT I do (cable replacement, etc.) I cannot get the write speeds anywhere near the read speeds.

My set-up is as follows:

• Motorola NVG589 (uverse gateway, gigabit lights active)
• Synology ds207+
• iMac (Snow Leopard, 10.6.8)
• Macbook Pro (Yosemite, 10.10.1)

For example, from the Macbook to the iMac I see the following:

Wifi (802.11n)

• Write Time = 109.0403477 Seconds
• Write Speed = 7.3367360 Mbps
• Read Time = 14.7147356 Seconds
• Read Speed = 54.3672720 Mbps

Thunderbolt gigabit ethernet

• Write Time = 12.4143649 Seconds
• Write Speed = 64.4414800 Mbps
• Read Time = 1.0175524 Seconds
• Read Speed = 786.2002960 Mbps

I can't for the life of me figure out WHY the numbers are so ridiculously different. Im happy with the read speed obviously (it's not ideal, but it's pretty fast), but the write speeds just suck. If I could bring them inline with my read speeds I'd be happy, but can anyone tell me why this might be happening? The thing that gets me is that it happens on 802.11n AND gigabit... if it was just wired I could assume maybe I had a bad 3/6 pin somewhere, but the wifi seems to point to something else...

Thanks in advance for any help.

rt

 

[htismaqe]

It takes a lot longer to write data to a drive than to read data. The speeds aren't ever going to be similar, write vs. read.

Furthermore, if you're using 5400rpm drives, that's going to significantly affect write speeds.

Also, I wouldn't trust the Totusoft LAN Speed Test on Mac, I've had issues with it reporting speeds that aren't just wrong, they're impossible. For example, I once had it report a read speed of 11,500 Mbps...

 

[rtilghman]

It takes a lot longer to write data to a drive than to read data. The speeds aren't ever going to be similar, write vs. read.

Furthermore, if you're using 5400rpm drives, that's going to significantly affect write speeds.

Also, I wouldn't trust the Totusoft LAN Speed Test on Mac, I've had issues with it reporting speeds that aren't just wrong, they're impossible. For example, I once had it report a read speed of 11,500 Mbps...

Thanks for the reply. That all makes sense, but shouldn't be a little bit higher than 64Mbps? When I test against a shared 7200 2tb WD drive (through the iMac) I get similar speeds on the gigabit connection, and when I do it the other way (iMac to Macbook) it's comparable. Just seems like a really slow write speed, even if you assume LAN Speed Test isn't 100% accurate.

The issue is that I don't really know enough about typical write/read speeds to be able to benchmark it.

Thanks,
rt

 

[azazel1024]

It takes a lot longer to write data to a drive than to read data. The speeds aren't ever going to be similar, write vs. read.

Furthermore, if you're using 5400rpm drives, that's going to significantly affect write speeds.

Also, I wouldn't trust the Totusoft LAN Speed Test on Mac, I've had issues with it reporting speeds that aren't just wrong, they're impossible. For example, I once had it report a read speed of 11,500 Mbps...

That isn't true at all. Read and write speeds on mechanical hard drives are generally within about 5% of each other.

I also wouldn't trust an artificial test here. Try real data transfers.

Also, keep in mind that with Snow Leopard there, you might be having SMB issues, as Apple has generally done a piss poor job of incorporating it in to OSX, at least until very recently.

 

[htismaqe]

That isn't true at all. Read and write speeds on mechanical hard drives are generally within about 5% of each other.

Not when you factor in OS, CPU, FS drivers, and other overhead. He's using a SOC NAS, not a server. While it is true that read/write on a physical bare drive would be roughly the same, that will almost never be the case with a consumer/SMB NAS.

I also wouldn't trust an artificial test here. Try real data transfers.

Absolutely agree.

Also, keep in mind that with Snow Leopard there, you might be having SMB issues, as Apple has generally done a piss poor job of incorporating it in to OSX, at least until very recently.

SMB2 is STILL broken, even on Yosemite 10.10.1. Sometimes it flies. Sometimes it gets 99% complete with a 100GB file transfer and then errors out with a "file is in use" error.

I would recommend using SMB1 (by prepending CIFS://) at the very least and if your NAS supports it, use AFP.

 

[azazel1024]

Ugh (on the state of SMB and OSX. A small part of the reason why I refuse to touch it).

You have an excellent point on NAS writes. Not something I was considering (I was thinking in terms of the drive of course). Writes do often lag 20-60% depending on a lot of things (and the DS207+ is not a particularly new, or from what I can recall, fast NAS).

 

[htismaqe]

Yeah the state of SMB on OS X is pretty sad, honestly. Fortunately, most of the major NAS vendors still support AFP so it's very workable.

The OP didn't specify what FS he's using. A lot of people forego the recommended FS (usually EXT3/4) for NTFS because they think they might have to connect the volume to a PC some day. From a performance standpoint with most SOC NAS, that's the worst possible thing you could do.

 

[rtilghman]

Thanks for all the insight and replies, great stuff.

To the comments about the NAS, I didn't actually provide any details on the Synology transfers... all those rates were transfering between Yosemite (Macbook) and Snow Leopard (iMac). Interestingly when I transfer to a USB2.0 shared drive on the iMac (7200 rpm TB WD drive) I get the same rates... whether that's limited by the iMac I can't say, but it removes the iMacs drive as the weak link.

When I do transfers to the synology 207+ (which I've had for awhile, but which is gigabit enabled and has newer WD TB drives) I get half the rate I get to the iMac... about 350Mb read, 40Mb write. Again, a lot slower than I would expect, even with 5400rpm drives.

To the comments about SMB vs AFP, are you guys saying I should disable SMB across network (iMac and Macbook)? Not ideal, but I've been reading a little about the SMB2 issues on Macs recently and know what you're talking about.

Let me know any thoughts.

Thanks,
Rick

 

[htismaqe]

To the comments about SMB vs AFP, are you guys saying I should disable SMB across network (iMac and Macbook)? Not ideal, but I've been reading a little about the SMB2 issues on Macs recently and know what you're talking about.

For transfers between the two Macs, especially since one is Yosemite and the other is Snow Leopard, you should absolutely use AFP and forget SMB. You don't have to disable SMB, just don't use it. That means you can't browse to it in the Finder GUI, you'll have to connect to it manually.

On whichever machine is initiating the connection, right click on Finder and select "Connect to Server". In the Server Address field, type afp:// followed by the IP address and path of your shared folder on the other machine.

If your NAS supports AFP, you can use the same method. If your NAS doesn't support AFP for some reason (I'm pretty sure Synology does and has for a long time), use the prefix cifs://. This will cause SMB to default to SMB1.