On Oct 15, 2011, at 12:31 PM, Toby Thain wrote:
> On 15/10/11 2:43 PM, Richard Elling wrote:
>> On Oct 15, 2011, at 6:14 AM, Edward Ned Harvey wrote:
>>>> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
>>>> boun...@opensolaris.org] On Behalf Of Tim Cook
>>>> In my example - probably not a completely clustered FS.
>>>> A clustered ZFS pool with datasets individually owned by
>>>> specific nodes at any given time would suffice for such
>>>> VM farms. This would give users the benefits of ZFS
>>>> (resilience, snapshots and clones, shared free space)
>>>> merged with the speed of direct disk access instead of
>>>> lagging through a storage server accessing these disks.
>>> I think I see a couple of points of disconnect.
>>> #1 - You seem to be assuming storage is slower when it's on a remote storage
>>> server as opposed to a local disk.  While this is typically true over
>>> ethernet, it's not necessarily true over infiniband or fibre channel.
>> Ethernet has *always* been faster than a HDD. Even back when we had 3/180s
>> 10Mbps Ethernet it was faster than the 30ms average access time for the 
>> disks of
>> the day. I tested a simple server the other day and round-trip for 4KB of 
>> data on a
>> busy 1GbE switch was 0.2ms. Can you show a HDD as fast? Indeed many SSDs
>> have trouble reaching that rate under load.
> Hmm, of course the *latency* of Ethernet has always been much less, but I did 
> not see it reaching the *throughput* of a single direct attached disk until 
> gigabit.

In practice, there are very, very, very few disk workloads that do not involve 
a seek.
Just one seek kills your bandwidth. But we do not define "fast" as "bandwidth" 
do we?

> I'm pretty sure direct attached disk throughput in the Sun 3 era was much 
> better than 10Mbit Ethernet could manage. Iirc, NFS on a Sun 3 running NetBSD 
> over 10B2 was only *just* capable of streaming MP3, with tweaking, from my 
> own experiments (I ran 10B2 at home until 2004; hey, it was good enough!)

The max memory you could put into a Sun-3/280 was 32MB. There is no possible way
for such a system to handle 100 Mbps Ethernet, you could exhaust all of main 
in about 3 seconds :-)

 -- richard


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