NAS Max Transfer Speed Questions.

[iwod]

I have had this questions for a few years and yet no one, no site, no forum on the internet seems to have an article on it. I hope someone with highly technical knowledge could answer my questions.

What is the maximum speed we can get from a NAS using CAT6 1 Gigibit Ethernet?

The article on SNB about Home Build NAS was the closest article relating to the topic. Assuming we have SSD Raid or even a Virtual Ram Drive, Quad Core CPU, 4Gb or higher Ram. a dedicated Gigibit Ethernet with Jumbo Frame support. Could we even achieve 80MB/s?

Looking at the chart on SNB, the fastest is WHS with write speed of 6x MB/s. Which is only half of the theoretical throughput.

So where is the bottleneck? CPU Power is one of the obvious answer as we see a clear relationship between Speed output and processing power.
But Why? We have been shouting about we have excessive CPU power for most of our use. And I can not believe such simple operation of transferring file over the network require more then 100% of a 500Mhz Pentium-M CPU workload. Any explanation as to why we need so much CPU power for such simple operation?

TCP/IP Stack. A lot of people will mention the overhead cost of using TCP/IP when transferring file. But how much of an overhead cost should we expect? Even at 30% overhead we could still get around 70Mb/s?

OS Protocol Problem? - With WHS we clearly see it is way faster then any other Linux Samba NAS. So is there overhead in Linux Samba implementation to Windows Machine as well?

[Bart]

This is not a direct answer to your question, but with my WHS I was able to sustain 70 - 75 MB/s write speed. It's logical I couldn't get any higher since my HD's aren't faster than that.

[iwod]

Originally Posted by Bart

This is not a direct answer to your question, but with my WHS I was able to sustain 70 - 75 MB/s write speed. It's logical I couldn't get any higher since my HD's aren't faster than that.

That is another point i want to make is that people constantly write transfer speed they are getting much higher then the one in shown in SNB chart.

[Tamarin]

In a NAS connected by a gigabit ethernet connection, you SHOULD be limited by the hard drive performance inside it. A modern hard drive (not a raptor or a SAS drive, just your run of the mill 320 or 500 gig SATA drive) can see sustained reads and writes from 60-75 MByte/s. This is a single drive, in optimal conditions. But there are many factors that can slow this down.

First is the processor in the NAS device. TCP overhead is can be demanding, some high-end server NICs have dedicated TCP offload engines just to reduce this burden.

Next is the hard drive fragmentation and location of the data on the platter. Data close to the outer edge can be read faster than data on the inner tracks. A good HDD review should show a curve that drops off as more data is read or written to the drive.

If the NAS is a RAID NAS, especially a RAID-5 NAS, you could see a performance hit, instead of a performance boost, because the controller doesn't have enough processing power to perform the parity calculations. This is one reason why many sysadmins insist on using high-end raid cards, even if the motherboard supports raid.

Basically, when it comes to NAS devices, there's no real way to know how a device is going to perform until it's tested. There are just too many variables. So keep reading SMB's NAS reviews. While their results aren't going to match yours perfectly, they'll at least help you pick out the good ones and avoid ones that aren't worth the sheet metal they're (hopefully) made from.

Tam

[thiggins]

Originally Posted by iwod

That is another point i want to make is that people constantly write transfer speed they are getting much higher then the one in shown in SNB chart.

Which chart? Remember that the bar charts are an average of multiple file sizes.

And if smaller file sizes are used, speeds will be much higher due to OS and NAS caching. That's why I added the "small file size mode" option to the charts.

[thiggins]

Don Capps, the creator of iozone and and expert on file systems, was kind enough to have a long chat about this the other day with me. Here are some key take-aways from the conversation:

- You should be able to get close to wire speed from a properly-designed NAS, even with a gigabit connection. 100 MB/s is achievable.

- You can have fast and you can have cheap. Most consumer NAS makers concentrate on keeping cost (and power consumption) down, which is generally the right trade-off for the market.

- SATA drives are an example of focusing on cost. They provide a lot of storage for relatively low money. But they have relatively short lives. They also are terrible when it comes to random access performance vs. sequential.

- RAID controllers that can handle a 100 MB/s rate don't come cheap. For example, a 3ware 4 channel 9500 series RAID controller will cost $350 - $400, but will do 100 MB/s RAID 5 writes. The 9650SE 4 channel controller will deliver over 800MB/s RAID 6 reads and 600MB/s RAID 6 writes and sells for about $400.

So, the technology is readily available for gigabit "wire speed" NASes. But that's not the direction that consumer NAS manufacturers are going.

[iwod]

If we look at the graph in the new Intel SS4200-E Entry Storage System slidshows, It shows all three , Iomega, Synology and Intel drop to mere 25MB/s at the end when file size are big. Which means they are all limited to 25MB/s.

Surely Raid 5 or HDD isn't a problem as 25Mb/s is very slow speed.
Processor could be a problem but would a Core2Quad improve it by much?
( Intel SS4200-E Entry Storage System is nothing more then a entry level computer with custom casing )

You see, 25MB/s is very far away from 80MB/s. So where is this bottleneck?

[thiggins]

In the SS4200-E, I think it's doing software RAID. So probably in the CPU and software.

[G_E_M_S]

Originally Posted by thiggins

- RAID controllers that can handle a 100 MB/s rate don't come cheap. For example, a 3ware 4 channel 9500 series RAID controller will cost $350 - $400, but will do 100 MB/s RAID 5 writes. The 9650SE 4 channel controller will deliver over 800MB/s RAID 6 reads and 600MB/s RAID 6 writes and sells for about $400.

And what about the HighPoint RocketRAID 2640x4?
It cost about 180$ and can do 501Mb/s Reads and 846Mb/s writes...
Looks good, what do ya think?

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What hardware specification should i use in order to achieve 100mb/s, using FreeNAS software raid 5 configuration???

[iwod]

Originally Posted by thiggins

In the SS4200-E, I think it's doing software RAID. So probably in the CPU and software.

For the past years people have been shouting that we have excess amount of CPU power. And yet we cant do raid5 with more then 25MB/s in software mode?

Which doesn't sound logical to me at all.