zfs receive stalls whole system

[Fabian Keil]

rainer at ultra-secure.de wrote:

> Am 2016-05-17 10:27, schrieb Fabian Keil:
> > Rainer Duffner <rainer at ultra-secure.de> wrote:
> >   
> >> I have two servers, that were running FreeBSD 10.1-AMD64 for a long 
> >> time, one zfs-sending to the other (via zxfer). Both are NFS-servers 
> >> and MySQL-slaves, the sender is actively used as NFS-server, the 
> >> recipient is just a warm-standby, in case something serious happens 
> >> and we don’t want to wait for a day until the restore is back in 
> >> place. The MySQL-Slaves are actively used as read-only servers (at the 
> >> application level, Python’s SQL-Alchemy does that, apparently).
> >> 
> >> They are HP DL380G8 (one CPU, hexacore) with over 128 GB RAM (I think 
> >> one has 144, the other has 192).
> >> While they were running 10.1, they used HP P420 RAID-controllers with 
> >> individual 12 RAID0 volumes that I pooled into 6-disk RAIDZ2 vdevs.
> >> I use zfsnap to do hourly, daily and weekly snapshots.  
> > [...]  
> >> Now, when I do a zxfer, sometimes the whole system stalls while the 
> >> data is sent over, especially if the delta is large or if something 
> >> else is reading from the disk at the same time (backup agent).
> >> 
> >> I had this before, on 10.0 (I believe, we didn’t have this in 9.1 
> >> either, IIRC) and it went away in 10.1.  
> > 
> > Do you use geli for swap device(s)?  
> 
> 
> Yes, I do.
> /dev/mirror/swap.eli		none	swap	sw		0	0
> 
> Bad idea?

It can cause deadlocks and poor performance when paging.

This was recently fixed in ElectroBSD and I intend to submit
the patch in a couple of days after a bit more stress testing.

The patch is already available at:
https://www.fabiankeil.de/sourcecode/electrobsd/GELI-Use-a-dedicated-uma-zone-for-writes.diff

Fabian
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