I will make this change on 2 exchange servers. What could be the risk. I don't want to lose the server.what you've experienced is a problem, or what may be the tiniest scenario. could there be any bug? when I change the SCSI Disk Controller driver.
Your last sentence indicates that you havent read the howto carefully or the howto is not detailed enough. There is no need for "changing" the driver because:
During your VM is up and running you add a additional 1G (thin) vDisk with a scsi:X:0 which automatic adds a additional scsi controller and you change it from the default (lsi) to para virtual. Since you already have orignal VMware Tools installed the windows driver for the para scsi controller is already there and with new added vDisk which is vissible in the windows disk management the driver is actived within the windows registry.
So shutdown your VM and change the existing scsi controller to scsi para and fire up the VM again. It will boot without A problem. After successfuly login you can remove the extra added vDisk from the VM. Technicly you can removed in earlier within the same step when changing the controllers. Done that couple of times and never something goes wrong.
Today we have VM templates which use the scsi para from begining.
BUT......... i dont suggest to change the scsi controller for your windows boot disk(c:) anymore. Why?.... because if you have the need to deinstall the VMware tools for what ever reasons and you reboot your systems you will get the BSOD named 7B for sure. Because the deinstallation also removes the windows driver from the system and windows OS cant start anymore. Now you have to remember the default type of scsi controller and change it back to LSI and windows can boot again. Well.. this can be a huge surprise for your co-workers :smileysilly:
Note: A lot of storage vendors suggest to add multible scsi controllers and add a single vDisk to each for performance reasons in their vSphere best practices.
sorry , why do you say don't change ? I want to change to VMware Paravirtual . I have the problem on the server and microsoft said the following. do you think I'm doing something wrong. i think i should do vmware paravirtual
''Windows CACHE MANAGER is the LSI_SAS driver, which is the main reason why delays occur on this driver and the VMWARE drivers also recommended to update. We see disk I/O requests pending in the LSI storage driver lsi_sas.sys targeted for VMWare virtual disks. This is causing cache manager write throttling (i.e. we have many dirty cached pages that need to be flushed to disk first) which means that any writes will be deferred (delayed) until the number of dirty pages is reduced. This is causing other threads to block while trying to write to the system cache including Exchange DAG management threads hence it crashed the system''
If you're having a problem and you need to change it, that's your decision. You've been provided a how-to blog which illustrates the process. The only thing I'd add is make sure you have no snapshots on this VM so as not to complicate the process. As with all disk-based manipulations, ensure you have a good, full backup of your Exchange data in case something goes wrong.
As mentioned we alway use multible SCSI Controllers within a VM as soon we have a need for a 2nd. vDisks
for an example. Yes for SCSI:1-3 we use VMware para scsi kontroller and the SCSI:0 stays on the VM/OS default.