[Discuss] A really interesting chain of functionality

[markw at mohawksoft.com (Mark Woodward)]

On 09/25/2011 10:49 AM, Edward Ned Harvey wrote:
>> From: discuss-bounces+blu=nedharvey.com at blu.org [mailto:discuss-
>> bounces+blu=nedharvey.com at blu.org] On Behalf Of Mark Woodward
>>
>> Has anyone played with LVM and iSCSI? The ability to create an arbitrary
>> block device and map it to a shareable LUN is interesting, don't you
> think?
>
> Personally, I do the same thing in ZFS using zvol's for improved performance
> and reliability and ability to snapshot.  (LVM snapshot is a terrible
> thing.)

Curious, have you done any serious benchmarking on LVM and snapshots? If 
so, I'd like to know about some of your tests.  I have been avoiding LVM 
for a while for performance concerns, but with quad core systems 
practically the baseline, a little extra CPU doesn't seem expensive any 
more. The features it gives you are pretty good.

I have to inspect the code to see how snapshots are implemented, it 
shouldn't be too costly after you modify a particular block for the 
first time. I can see a slowdown because of "copy on write" for 
snapshots, but it shouldn't be too too bad. Also, I'm not sure how it 
manages multiple snapshots there is a right way and a wrong way, I hope 
they did it the right way, but after your comment I'm dreading the 
actual answer.

Is ZFS prime-time ready for Linux? If so, do you have any insights about 
pros and cons for LVM?