I installed ZeXtras Migration tool on a Centos 5, Zimbra 7.2.2. When I started export process, it takes long time, and the scan speed from the log shows it is very slow, only 4 per second, and it takes several hours to finish one account:
Operation log path: /opt/zimbra/log/zextras_ZxBackup_doExport_ebd5d68f-b7e1-456f-91b0-d1afa574f53e.log
Account scanned: 2/107
Account new: 3
Item scanned: 45500
Item new/unique: 44411/39823
Items per second: 4
processor Intel(R) Xeon(R) CPU E5405 @ 2.00GHz
8GiB System Memory
/dev/sda6 271G 46G 212G 18% /
/dev/sda5 46G 323M 43G 1% /var/log
/dev/sda4 118G 9.1G 103G 9% /usr
/dev/sda1 927M 30M 850M 4% /boot
tmpfs 3.9G 0 3.9G 0% /dev/shm
/dev/md0 5.5T 1.6T 3.9T 30% /raid5-drive
/raid5-drive/opt 5.5T 1.6T 3.9T 30% /opt