What's the NAS bottleneck?

Hi all,
I consider buying a NAS (see other thread) but can't understand why current devices are so slow.
-Current 7200rpm sata hard disks can do 100 MB/s
-A gigabit network can handle 100 MB/s without any problem

BUT

-Ethernet hard drives go up to 6-7 MB/s
-The best NAS boxes available go up to 25-30 MB/s

WHY?

How to break that barrier?
Would a server (home-made or dell poweredge t100 or something like that) with SAS 15K drives and a RAID deliver those 100 MB/s (for large files)?

The problem is generally not the drives or hardware, but mostly the Windows SMB protocol.

Even a high-end Dell/HP/IBM server with SAS drives and PCIe server networking cards cannot sustain more than about 35-40 MB/sec across a Gigabit network to a single client. The SMB (Windows file sharing) protocol is inefficient and just can't sustain any more.

This has been somewhat rectified in Windows Server 2008 and Vista SP1. If you have a Vista SP1 client talking to Windows Server 2008, you can actually get 65-70 MB/sec.

Now, of course, there are cheap NAS units on the market that simply don't have enough processing power to run the SMB protocol very well, and will give low performance anywhere from 5-15 MB/sec.

The only way you can get faster transfers over Gigabit Ethernet is to use a protocol other than SMB.

I have a server connecting to a SAN unit running the iSCSI protocol over dual Gigabit Ethernet connections (bonded together using the iSCSI multipath I/O protocol, MPIO). I routinely can transfer data at 225 MB/sec over this connection.

The problem with iSCSI is that it is not a file system level protocol like SMB, it is a block level protocol. As such, multiple clients cannot share access to the same volume, because iSCSI has no mechanism for arbitrating access to files.

The easiest and surprisingly, most accurate method is to just copy a large file (a DVD .iso image is ideal) and time it. Then divide it out (file size in bytes / seconds to transfer = bytes/second). This is the method I use, and is accurate within about .1 MB/sec.

I like this way rather than a synthetic benchmark because this gives a real-world transfer rate that includes the Windows Explorer interface and its buffering, and the SMB server and its buffering. Synthetic benchmarks will generally bypass something in this path and end up with a somewhat inflated number.

Another method I use is to build an .iso file with ImgBurn. Using a folder on your local machine that contains DVD files (the VIDEO_TS folder), do a build operation with ImgBurn and save the resulting .iso file on the server. This is essentially a file copy operation and virtually no CPU performance comes into play. ImgBurn will give you a real-time transfer rate during the build process as well as an average transfer rate after its done. From my workstations to my server (XP and 2003) I get about 38 MB/sec when I do this operation.

Linux's (and most *nix's) native file sharing protocol is NFS. NFS is quite a bit faster than SMB.