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[Discuss] Thin Provisioned LVM

On 3/12/2015 8:46 AM, markw at wrote:
> (1) If someone could point me in the direction of documentation on how to
> get ZFS to update file or zvol blocks IN PLACE, i.e. without going through
> the ZIL, then cool, I would really find that helpful.

See, this is what Ned is on about. There are two things that you've 
written here that demonstrate a significant lack of understanding of ZFS.

First is the ZIL. ZFS always has a ZIL. On a simple system the ZIL is on 
the data vdevs. In a high performance pool the ZIL is a dedicated 
low-latency device like a RAM-based SSD (optimally a mirrored pair). But 
regardless, there's always a ZIL.

Second is that you don't tell ZFS to update in place. That's not how one 
does things with ZFS. The ZFS way is to enable deduplication and 
compression. I *DID* point you at these and I explicitly called out 
deduplication as the solution to the rampant space gobbling problem that 
you described. You chose to brush all of it off as "ZFS is stupid".

No, it isn't.

> First, on Linux, currently, ZFS does not cluster across multiple systems,
> so there's one instance. That means you can't create fully redundant
> applications on Linux using ZFS.

I don't know where you picked up this idea but it's very wrong. I've 
designed, deployed and managed fully redundant HA systems without 
cluster-aware file systems. Cluster-aware file systems are just of 
several solutions to the problem of shared storage.

Rich P.

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