Comments on: SSD + VAAI = TRIM ? http://www.hypervisor.fr/?p=4847 French Bare-Metal weblog Fri, 30 Jul 2021 14:16:54 +0000 http://wordpress.org/?v=2.9.2 hourly 1 By: Andreas Peetz http://www.hypervisor.fr/?p=4847&cpage=1#comment-2940 Andreas Peetz Wed, 04 Sep 2013 13:44:08 +0000 http://www.hypervisor.fr/?p=4847#comment-2940 Hi Raphael, I thought you were talking about VMworld in San Francisco, but obviously you mean Barcelona. Yes, I will also be there! Maybe we can meet and together cross-examine Cormac ;-) ?! Regarding TRIM in VMs I'm pretty sure that this does not work. There is a VMware fling available to achieve space reclamation on disks that were thin provisioned at the storage array layer, see http://labs.vmware.com/flings/guest-reclaim. I'm not sure if it still works. And I don't think that it will be useful with SSDs. If the guest unmaps a block on its virtual disk (e.g. NTFS) it will still be allocated to the VMDK file at the host (VMFS) level and cannot really be unmapped there. At the VMFS level you can only unmap/trim blocks that do not belong to an existing VMDK file. At least I think so. It's hard and confusing to think through all the different layers of storage virtualization and abstraction ... Andreas Hi Raphael,

I thought you were talking about VMworld in San Francisco, but obviously you mean Barcelona. Yes, I will also be there!
Maybe we can meet and together cross-examine Cormac ;-) ?!

Regarding TRIM in VMs I’m pretty sure that this does not work. There is a VMware fling available to achieve space reclamation on disks that were thin provisioned at the storage array layer, see http://labs.vmware.com/flings/guest-reclaim. I’m not sure if it still works. And I don’t think that it will be useful with SSDs. If the guest unmaps a block on its virtual disk (e.g. NTFS) it will still be allocated to the VMDK file at the host (VMFS) level and cannot really be unmapped there. At the VMFS level you can only unmap/trim blocks that do not belong to an existing VMDK file.

At least I think so. It’s hard and confusing to think through all the different layers of storage virtualization and abstraction …

Andreas

]]> By: NiTRo http://www.hypervisor.fr/?p=4847&cpage=1#comment-2939 NiTRo Tue, 03 Sep 2013 23:16:37 +0000 http://www.hypervisor.fr/?p=4847#comment-2939 Hi Andreas, What a coincidence indeed! I didn't spoke to Cormac about that, i keep that one for VMworld because i'm sure i would have some juicy details i won't have by email or twitter :) Will you be there? I'm surprise no one else told about that BTW. I also got the idea to check what appends when you remove files in Windows 8 VM residing on SSD. Maybe the TRIM command is catch by the vmkernel ?! Hi Andreas,
What a coincidence indeed! I didn’t spoke to Cormac about that, i keep that one for VMworld because i’m sure i would have some juicy details i won’t have by email or twitter :) Will you be there?

I’m surprise no one else told about that BTW.

I also got the idea to check what appends when you remove files in Windows 8 VM residing on SSD. Maybe the TRIM command is catch by the vmkernel ?!

]]> By: Andreas Peetz http://www.hypervisor.fr/?p=4847&cpage=1#comment-2938 Andreas Peetz Tue, 03 Sep 2013 17:57:14 +0000 http://www.hypervisor.fr/?p=4847#comment-2938 Hi Raphael, what a coincidence! I am running an ESXi host on SSDs since a few days and was now researching on the issue of TRIM support in ESXi. I stumbled over the possible relationship to SCSI UNMAP feature and finally discovered the same than you: My SSDs support the VAAI Delete Status and I can run "vmkfstools -y" on them! Have you talked to Cormac about that, and did he confirm that this is indeed equivalent to TRIM? Thanks and best regards Andreas Hi Raphael,

what a coincidence! I am running an ESXi host on SSDs since a few days and was now researching on the issue of TRIM support in ESXi. I stumbled over the possible relationship to SCSI UNMAP feature and finally discovered the same than you: My SSDs support the VAAI Delete Status and I can run “vmkfstools -y” on them!

Have you talked to Cormac about that, and did he confirm that this is indeed equivalent to TRIM?

Thanks and best regards
Andreas

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