[Users] flashcache

[Pavel Snajdr]

On 07/08/2014 07:52 PM, Scott Dowdle wrote:
> Greetings,
> 
> ----- Original Message -----
>> (offtopic) We can not use ZFS. Unfortunately, NAS with something like
>> Nexenta is to expensive for us.
> 
> From what I've gathered from a few presentations, ZFS on Linux (http://zfsonlinux.org/) is as stable but more performant than it is on the OpenSolaris forks... so you can build your own if you can spare the people to learn the best practices.
> 
> I don't have a use for ZFS myself so I'm not really advocating it.
> 
> TYL,
> 

Hi all,

we run tens of OpenVZ nodes (bigger boxes, 256G RAM, 12cores+, 90 CTs at
least). We've used to run ext4+flashcache, but ext4 has proven to be a
bottleneck. That was the primary motivation behind ploop as far as I know.

We've switched to ZFS on Linux around the time Ploop was announced and I
didn't have second thoughts since. ZFS really *is* in my experience the
best filesystem there is at the moment for this kind of deployment  -
especially if you use dedicated SSDs for ZIL and L2ARC, although the
latter is less important. You will know what I'm talking about when you
try this on boxes with lots of CTs doing LAMP load - databases and their
synchronous writes are the real problem, which ZFS with dedicated ZIL
device solves.

Also there is the ARC caching, which is smarter then linux VFS cache -
we're able to achieve about 99% of hitrate at about 99% of the time,
even under high loads.

Having said all that, I recommend everyone to give ZFS a chance, but I'm
aware this is yet another out-of-mainline code and that doesn't suit
everyone that well.

snajpa