On 08/06/2011 09:30 PM, John A. Sullivan III wrote:
> On Sat, 2011-08-06 at 21:40 +0200, Eugen Leitl wrote:
>> I've recently figured out how to make low-end hardware (e.g. HP N36L)
>> work well as zfs hybrid pools. The system (Nexenta Core + napp-it)
>> exports the zfs pools as CIFS, NFS or iSCSI (Comstar).
>>
>> 1) is this a good idea?
>>
>> 2) any of you are running vserver guests on iSCSI targets? Happy with it?
>>
> Yes, we have been using iSCSI to hold vserver guests for a couple of
> years now and are generally unhappy with it. Besides our general
> distress at Nexenta, there is the constraint of the Linux file system.
>
> Someone please correct me if I'm wrong because this is a big problem for
> us. As far as I know, Linux file system block size cannot exceed the
> maximum memory page size and is limited to no more than 4KB.
I'm pretty sure it is _only_ limited by memory page size, since I'm
pretty sure I remember that 8KB blocks were available on SPARC.
> iSCSI
> appears to acknowledge every individual block that is sent. That means
> the most data one can stream without an ACK is 4KB. That means the
> throughput is limited by the latency of the network rather than the
> bandwidth.
Hmm, buffering in the FS shouldn't be dependant on the block layer
immediately acknowledging unless you are issuing fsync()/barriers. What
FS are you using on top of the iSCSI block device and is your
application fsync() heavy?
Gordan
Received on Sat Aug 6 21:37:42 2011