system hangs during dump + compress > usb2-drive

[Jin Guojun]

________________________________
From: Xin Li <delphij at delphij.net>
To: Jin Guojun <jguojun at sbcglobal.net>
Cc: questions at freebsd.org; hackers at freebsd.org
Sent: Sun, September 30, 2012 1:07:40 PM
Subject: Re: system hangs during dump + compress > usb2-drive

On 9/29/12 10:49 PM, Jin Guojun wrote:
> In FreeBSD 8.3 release (possibly in earlier release),  dump a file
> system has 2-3GB or more content can cause system hang in a
> specific  case (pipe to compression):
> 
> dump FS-on-SATA-drive >  usb-drive         OK dump FS-on-SATA-drive
> | anyCompress >  sata-drive         OK mv a-large-dump-file from
> STAT drive to a USB drive         OK dump small-FS-on-SATA-drive |
> anyCompress >  usb-drive         OK small -- 1.8GB or less dump
> large-FS-on-SATA-drive | anyCompress >  usb-drive         hang 
> content is 3GB or larger (did not try around 2GB yet)
> 
> When system hangs, no sub system, such video, network, etc, will
> function. Typically, the unfinished compressed dump file is around
> 1.5-2.7GB, so guessing dumped file content is close to or over 2GB
> when failure occurred.
> 
> Has anyone encountered the same problem?
> 
> Because this usually takes a few hours to occur, this is hard to
> watch how/when it happens. Is any way to debug or determine what
> status the system is?

For starters I'd use a different console for doing procstat -kk -a and
see what the system is doing.  (Perhaps also top)

I *think* that if it's just hanging for some time, it's probably
because the system is trying to take a snapshot?  It takes time on UFS
when creating and removing the snapshot.  Just a guess...

Cheers,

---------------

Not sure how to use a different console. No tty is functioning (neither ttyv? 
nor over network).
You are right on a different case --

            mount /dev/da0s4d /mnt    # mount a usb drive
             cd /mnt
            ssh remote-liux-host "tar -cf - 8GB_FS" | tar -xf -

In this case, doing ls -l /mnt or df will hangs, but system is still alive. The 
network is 45Mbps.
I have no idea how long it took the tar to finish since machine is 60 km away.
When I left there last Friday, only 400MB was done in one hour. I will get the 
processing time tomorrow.
The problem we can see now is that tar (probably the pipe) process only finish 
with 4GB.
# df
Filesystem            1K-blocks       Used      Avail Capacity  Mounted on
/dev/ad4s3a              1012974    355348     576590    38%    /
devfs                          1         1          0   100%    /dev
...
/dev/da0s4d           1027486774   4198246  941089588     0%    /mnt

So, I suspect this is a pipe problem, not a compress issue.