How to slow down plex resync or other VERITAS Volume Manager copy operations

Problem

How to slow down plex resync or other VERITAS Volume Manager copy operations

Solution

The speeds of a plex resync and other VERITAS Volume Manager (VxVM) copy operations like vxrelayout are governed by 2 parameters:  iosize and slow.

The optional parameter iosize defines the size of data blocks to be copied [default=32k]. Theoretically, the greater the block size the faster the copy process. For large values of iosize it can have a detrimental effect on other processes doing I/O.

The optional parameter 'slow'  defines the number of milliseconds the copy process will pause until the next data block of size iosize gets processed [default=0].

The most effective way to lower the resync speed is to set the optional slow parameter:   slow=iodelay


Case A:  lower the resync speed of a running process:

1. Check throttle setting [parameter slow]:

# vxtask -l list
Task:      179 RUNNING (Parent: 178)
Type:      ATCOPY
Operation: PLXATT Vol opt Plex opt-02
Started:   Tue Mar 12 16:20:34 2002
Throttle:  0
Progress:  5.84% 612560 of 10487232 Blocks
Work time: 38 seconds (10:12 remaining)
#

2. Increase the throttle setting:

# vxtask set slow=50 179

# vxtask -l list 179
Task:      179 RUNNING (Parent: 178)
Type:      ATCOPY
Operation: PLXATT Vol opt Plex opt-02
Started:   Tue Mar 12 16:20:34 2002
Throttle:  50
Progress:  36.20% 3796880 of 10487232 Blocks
Work time: 3 minutes, 46 seconds (44:38 remaining)
#



Case B:   start a new VxVM copy process with a lowered resync speed:

e.g: vxrecover -o slow=50 -sb
    vxplex -g <DG> -o slow=30 att opt opt-02
    vxassist -g <DG> -o slow=10 mirror opt

Check the new throttle setting [parameter slow] with vxtask -l list.

The optional parameter slow is accepted for a wide range of commands:  
vxvol, vxplex, vxrelayout, vxassist, vxrecover.

If the resync speed of a process was reduced by too much it can always be set to a more appropriate level using the vxtask command as shown in case A.







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