[Info-vax] Reclaim disk space for a 3PAR Storage Box

[Ian Miller]

On Friday, August 27, 2021 at 1:50:16 PM UTC+1, bruno.... at gmail.com wrote:
> Dear all, 
> I would like to expose you an issue with the hope that you can help me to solve it in the best way. 
> 
> We have OpenVMS 8.4 clusters connected to a full SSD 3PAR storage box via a FC SAN. 
> 
> We have thin provisioning activated on the 3PAR meaning that we make some “overbooking” with the disk size. We can’t have all disks presented with 100% used space because we don’t have that physical disk space available. 
> 
> The 3PAR use the free space available on each disk as a common free space pool available to ensure the used size increase of all the disks. (Don’t ask me more, I’m OpenVMS system manager, not Storage manager) 
> 
> On OpenVMS, a simple DELETE doesn’t tell to the 3PAR that this deleted area is available to be part of the common pool. The 3PAR still considers that location as used. 
> 
> With DELETE/ERASE, “the storage location is overwritten with a system specified pattern so that the data no longer exists.” 
> 
> So, I had to implement something that will make an erase operation. 
> 
> I though to put in place a SET VOLUME /ERASE_ON_DELETE but I’m afraid that severe performance decreases will occur, especially on heavy used disks (creating and deleting a lot of files). 
> 
> So I made the choice of DELETE/ERASE. 
> 
> Twice a week, I create 10 MB dummy files until the disk if 95% Full. Then I initiate a DELETE/ERASE of those files. The delete is made one by one to verify that something else is not busy to fill in the disk. If it is the case, I make a simple DELETE for the rest of the files which is more performant. 
> 
> I don’t create a big file because the DELETE/ERASE could take many time and the size is not available during the operation. This could compromise the used space increase requested by the application. 
> 
> My problem is that for big disks (800GB) with a low used space, we create thousands and thousands of files and the DELETE/ERASE takes days. 
> 
> Do you see another way of working ? 
> 
> I checked the defragmenter, there is a /CONSOLIDATE_FREESPACE but not a “/ERASE_FREESPACE” option 
> 
> I was hoping to find something in OpenVMS that could act in background, all the time without impacting the performances. 
> 
> Thanks for your help. 
> 
> Seghers Bruno
In the VMS84I_SYS-V0700 and VMSA_SYS-V0700 ECO kits, new features have been added to allow HPE OpenVMS to tell storage controllers to deallocate space on thin-provisioned volumes
–OpenVMS can now use the SCSI UNMAP function for this purpose.