You can run the below script in the Manage Jenkins ? Scripts Console for deleting the workspaces of all the jobs at one shot. We did this to clean up space on the file system.
import hudson.model.*
// For each project
for(item in Hudson.instance.items) {
// check that job is not building
if(!item.isBuilding()) {
println("Wiping out workspace of job "+item.name)
item.doDoWipeOutWorkspace()
}
else {
println("Skipping job "+item.name+", currently building")
}
}