RELENG_5, snapshots and disk lock time

Dmitry Morozovsky marck at
Mon Mar 7 07:07:06 PST 2005

Following up to myself

DM> XL> > dumping the snapshot of 140G ufs2 fyle system under contemporary RELENG_5 I 
DM> XL> > found that during mksnap_ffs file system is unresponsible even for reading for 
DM> XL> > more than 3 minutes (it's on modern SATA disk with 50+ MBps linear transfer). 
DM> XL> > Is it normal?
DM> XL> 
DM> XL> mksnap_ffs is expected to suspend your write access, but I think 3
DM> XL> minutes is too long for a 140G file system.  Would you please send the
DM> XL> dumpfs output of the said file system?
DM> Well, as I said, it was even for read access. I checked this with the simple 
DM> shell script
DM> #!/bin/sh
DM> while true; do
DM> 	sleep 5
DM> 	date
DM> 	ls /lh/.snap
DM> done

It seems accessing snapshot directory is blocked for much more time than to 
other fs parts. Changing ls line to ``ls /lh'' leads to 

Mon Mar  7 18:02:58 MSK 2005
backup  home    local   pgsql   ports   src
Mon Mar  7 18:03:41 MSK 2005

so file system has been locked for approx 45 seconds. This seems more 
reasonable, but still seems a bit too long for me.

D.Marck                                     [DM5020, MCK-RIPE, DM3-RIPN]
*** Dmitry Morozovsky --- D.Marck --- Wild Woozle --- marck at ***

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