Areca vs. ZFS performance testing.

[Danny Carroll]

Koen Smits wrote:
> Please let us know what Areca says about the caching.
> If you ask me, these results definitely are cached.
> 


Sorry for the delay.

Areca got back to me.  It took a few days but I got someone who seemed
to know what they were talking about.

>From what I can gather the cache is always on.  You can configure it to
be writeback or writethrough in some situations but when that is not an
option, writethrough is the default.  I could not get any information
about read caching although I might send an email to see what happens.

Here is the transcript of the conversation:
Me:
I have a rather simple question about the 1231 controller.
Can you please explain the difference between using disks in JBOD mode
and using disks in passthrough mode.   I have a feeling that the
controller uses it's onboard cache when in passthrough mode.  Is this
the case?

Also, are both read and write operations cached?

Areca Support:
Dear Sir,
the only difference is
in JBOD mode, controller configure all drives as passthrough disk.
in RAID mode, you have to configure passthrough disk by yourself in RAID
mode

in other words, you can use raid with passthrough disks at saem time in
RAID mode but JBOD mode not.

Me:
So does that mean if I use passthrough, I am not protected by the
cache/battery backup?  I ask because there is an option for cache mode
when creating a passthrough disk.  i.e. Write-Back or Write-Through

Areca Support:
Dear Sir,
in JBOD mode, the default setting writeback mode.

with writeback mode, you will need a battery module to protect the data
remain in cache in case you got a power failure problem.

Me:
And so in Passthrough mode I am still protected with the battery backup?

So JBOD = WriteBack Cache with protection of the battery backup.
Passthrough = WriteBack or WriteThrough also with protection of the
battery backup.

Is this correct?

Areca Support:
Dear Sir,
if you have battery module attached, yes.