[zfs-discuss] Re: Copying a file from one ZFS to another starves all other processes

Ryan How ryan at zbit.net.au
Wed May 22 02:50:01 EDT 2013

I've compiled against Ubuntu Raring Kernel (GIT Head).

Just has default kernel config + a few filesystems + network drivers + 

Seems to be a bit more stable than it was before. But still get the same 
issue. Maybe I should set up a straight ubuntu box and see if it works.

On a side note, if there any way to throttle a cp ?. Maybe if I throttle 
it (I shouldn't have to!) at least it won't kill the system. ionice 
doesn't seem to make any difference.

Thanks, Ryan

On 20/05/2013 10:50 AM, Ryan How wrote:
> BTW, I'm not overlaying ZFS with aufs or anything, they don't interact 
> at all on the system.
> On 20/05/2013 10:47 AM, Ryan How wrote:
>> Thanks,
>> I'm running slackware 14.0, and am compiling ZOL with the "Generic 
>> RPM" KMOD method. I've just downloaded the ubuntu raring kernel 
>> sources and will try that. Most people seem to be using that and it 
>> is working. I'm using Aufs too, so I need to compile a custom kernel 
>> (But not doing any crazy configuration or anything). Seems that 
>> ubuntu raring already has it patched in :)
>> Thanks, Ryan
>> On 19/05/2013 11:36 PM, RangerRick wrote:
>>> Hi Ryan,
>>> What version of Linux are you running?  We have many hundreds of 
>>> customers using ZOL with SoftNAS and have had no such issues with 
>>> ZOL on CentOS 6.x.
>>> However, I have seen something similar to what you describe occur 
>>> when files are copied to and from the LOCAL filesystem (non-ZFS) 
>>> only on a ZOL system.  Local filesystem caching appears to put 
>>> pressure on available memory, which in turn causes what appears to 
>>> be a lockup until that memory pressure is relieved.  We have not 
>>> observed this when the files being copied are ZFS to ZFS - only if 
>>> done on the root filesystem, which is non-ZFS.  As we do not use the 
>>> root filesystem for file sharing, we do not encounter this in practice.
>>> Rick
>>> On Friday, May 17, 2013 11:29:32 PM UTC-5, Ryan How wrote:
>>>     With all the ZFS problems I'm having, it seems that it must be a
>>>     problem
>>>     with my kernel or something, coz otherwise I'm sure there would
>>>     be a lot
>>>     more people posting issues on the mailing list and a lot less
>>>     people
>>>     using ZOL!
>>>     They all almost seem related to I/O scheduling and buffering
>>>     (well the
>>>     symptoms of it, not sure what the actual problem is)
>>>     One of the problems I'm having is when copying a file (cp fileA
>>>     fileB),
>>>     it basically starves everything else. Then my VMs (running as file
>>>     backed storage directly on ZFS) get corrupt filesystems
>>>     reporting that
>>>     the disk controller was not responding (I'm guessing because
>>>     they are
>>>     trying to write, get to response from the system, so the guest
>>>     things
>>>     the virtual disk is faulty)
>>>     Does anyone else get anything like this?
>>>     When copying as well, all the zfs commands are slow to respond (eg.
>>>     zpool iostat takes a few seconds to spit out any info)
>>>     Not using dedup or compression, machine has 32GB ram of which
>>>     6GB is
>>>     currently free (after running for a few hours)
>>>     I'm not really fussed if performance is slow (but performance is
>>>     actually quite good), but if I am doing more than 1 disk related
>>>     thing
>>>     at a time it is kinda useless.
>>>     Thanks, Ryan

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