I’m running xcp-ng 8.0. VM VDs are on NFS (TrueNAS).
So I have a CentOS VM with /home (ext3) on a local SSD SR (using an entire 480GB SSD), but the rest on NFS SR. df in CentOS reads /home as 11G used (3%), 400G available. But, df in the host with the uuid of SR (as well as looking at the SR in XenOrchestra, and XenCenter) as 281G used (68%), 138G available.
Basically, the reason I installed this drive in the first place was because I needed the i/o for a particular VM, and files (lots and lots of them) were going to be written/deleted, written/deleted, etc… which I understand could be torturous to an NFS SR.
So since the files are being deleted by a cron job in CentOS, 1) why are the OS and Xen showing such different values? I expect it’s because the OS deleting the file does not zero out the blocks on the SSD, or even the VD.
- Can someone explain what happens when you delete a file in a linux OS?
- Why isn’t the VD being updated, or is it more proper to ask, should the VD be updated?
- If the OS shows 3% usage, and the VD shows 68%, assuming I keep deleting the files, and /home in the OS stays at about 3%, but the VD grows and grows, what wil the VD actually do when it gets to 100%?
- Is there a better way to utilize this SSD for this purpose? Is passthrough a good choice here? If so, will df in the OS properly display accurate numbers? (I realize XO and xcp-Center will not be accurate, and will show 100% usage [according to Tom’s video])