kern.geom.raid3.syncs_per_sec=0

["José M. Fandiño"]

Accidentally I set this variable to 0 and it causes a hard lock (FreeBSD 
5.4-RELEASE-p2)

could someone check if this reproducible in their test machines so I can
open a pr?

	/-------/

Geom name: datos
State: COMPLETE
Components: 3
Flags: ROUND-ROBIN
GenID: 0
SyncID: 3
ID: 3217021940
Providers:
1. Name: raid3/datos
    Mediasize: 311491352576 (290G)
    Sectorsize: 1024
    Mode: r1w1e0
Consumers:
1. Name: ad4s2
    Mediasize: 155745676800 (145G)
    Sectorsize: 512
    Mode: r1w1e1
    State: ACTIVE
    Flags: DIRTY
    GenID: 0
    SyncID: 3
    Number: 2
    Type: PARITY
2. Name: ad5s2
    Mediasize: 155745676800 (145G)
    Sectorsize: 512
    Mode: r1w1e1
    State: ACTIVE
    Flags: DIRTY
    GenID: 0
    SyncID: 3
    Number: 0
    Type: DATA
3. Name: ad6s2
    Mediasize: 155745676800 (145G)
    Sectorsize: 512
    Mode: r1w1e1
    State: ACTIVE
    Flags: DIRTY
    GenID: 0
    SyncID: 3
    Number: 1
    Type: DATA