iSCSI vs. SMB with ZFS.

[Ivan Voras]

On 12/12/2012 17:57, Zaphod Beeblebrox wrote:

> The performance of the iSCSI disk is
> about the same as the local disk for some operations --- faster for
> some, slower for others.  The workstation has 12G of memory and it's
> my perception that iSCSI is heavily cached and that this enhances it's
> performance.  The second launch of a game ... or the second switch
> into an area (ie: loading a specific piece of geometry again) is very
> fast.

> The performance on the SMB share is abysmal compared to the
> performance on the iSCSI share.  At the very least, there seems to be
> little benifit to launching the same application twice --- which is
> most likely windows fault.

Think about what you have there:

With iSCSI you have a block device, which is seen on your workstation as
a disk drive, on which it creates a "local" file system (NTFS), and does
*everything* like it is using a local disk drive. This includes caching,
access permission calculations, file locking, etc.

With a network file system (either SMB or NFS, it doesn't matter), you
need to ask the server for *each* of the following situations:
	* to ask the server if a file has been changed so the client can use
cached data (if the protocol supports it)
	* to ask the server if a file (or a portion of a file) has been locked
by another client

This basically means that for almost every single IO, you need to ask
the server for something, which involves network traffic and round-trip
delays.

(there are smarter network protocols, and even extensions to SMB and
NFS, but they are not widely used)

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