Intermittent issues with reading files via SMB/CIFS

[bigE]

Hi! I am new to forum, and registered to ask of your help to resolve an issue I have.
I've got a server, consisting of the next components:
- two-socket Supermicro X9DRL-3F motherboard
- two E5-2630 CPUs
- 64GB RAM (ECC)
- 5x WD Red 3TB hard drives
- Nas4Free: 10.2.0.2 - Prester (revision 2268)

I've got the following extensions installed:
- Extended GUI
- Syncthing
- RRDGraphs
- EzPlex

The following services are enabled:
- CIFS/SMB shares
- bittorent (transmission)
- UPS

ZFS config:
- All 5 hard drives are bundled into a single raidz2 pool.
- there are multiple data-sets on this pool.
- one of the data-sets is shared via CIFS/SMB

Here is the issue:
I have two three laptops, trying to access the CIFS/SMB share:
- win7 lenovo carbon X1, which has been installed an running for almost two years
- win7 lenovo w530, fresh install
- macbook air.

Performance - with such hardware I would think I'd get around 100MBps performance (I have gigabit network), but reads reach maximum of 40MBps, and writes reach 60MBps.
Intermittent read errors: W530 and macbook air experience file read errors from CIFS/SMB shares - when reading a directory with hundreds of files, the copy or read operation would get stuck, and then OS reports that file can't be read. X1 laptop doesn't experience these issues - just the copy performance is slow.

What is wrong with my setup? Please help.
What logs do I need to enable to help you troubleshoot this issue?

Thanks!

[bigE]

So, after some more digging on forum, I found out that changing MTU on server may help with read errors.
And it did! Well, I will keep monitoring, as performance is still not the best.

[b0ssman]

go through this list step by step.
http://n4f.siftusystems.com/index.php/2 ... /comments/

and doesnt the macbook air just have wlan?

[KimmoJ]

RaidZ is not a very performance friendly setup. Writes, especially - RaidZ is like RAID5 in that every write has to happen to every single drive, so write speed will be about what a single drive can manage, and 40MB/sec on a WD Red isn't entirely out of the realm of possibility (it should write faster to begin with as it puts the data in your cache, and then slow down once the cache fills up).

Read speed should be faster though as it can read from all of them. So you probably should tune your CIFS settings. I'm not a Samba speed expert by any means, but do you have large read/write enabled in your CIFS settings? What size are your send/receive buffers? More is better, up to a point I guess. Have you enabled asynchronous I/O? Both those can speed things up.

[bigE]

go through this list step by step.
http://n4f.siftusystems.com/index.php/2 ... /comments/

and doesnt the macbook air just have wlan?

Thanks, b0ssman, I'll try these steps tonight.
You are right, I tested macbook air with wlan only.

So, here is interesting fact - yesterday after changing mtu on nas4free server to 1472, I tried some more file transfers, and with async IO disabled and large read/write enabled, I was able to max out the 1Gbit connection on my W530.
The read errors happen, but a lot less. I am able to transfer tens of gigabytes information, before experiencing error.

I'll reply back once I follow the instructions you referred to.