SSD and Virtual Machines

Hi,

what is the general belief about installing virtual machines on an SSD? Will this quickly wear down the SSD with all the writes on a single very large file? If I intend to use VMs, should I favor an mSata SSD and install the VM on an HDD?

Thanks for your input

 

SSD is perfect for the 'writes on a single very large file'. file is not an SSD thing, it is an OS thing. These writes are RANDOM in nature which SSD excels at.

The only thing that is not so good about VM is that for most VM, the 'close' window button usually means 'hibernation' of the client OS which means there would be some massive write(allocated memory of the guest OS) each time you do it.

If you don't close your VM frequently or make the 'close' as 'shutdown', SSD is perfect for VM.

 

isn't the vm mostly or all in ram anyways?

 

depending on how much RAM you have. Though contrary to common believe, Windows(or any OS for that matter) doesn't really write that much to the HDD/SSD. Most are small logging writes which won't do any ding to the SSD.

 

Several common VM operations can hit an SSD's P/E cycles hard:

1) Installing the guest OS. Can't be avoided, but a single Windows 7 install is 8-15 GB. Once you factor in installing SP1 and Windows Updates patches, the writes can add up pretty fast. Any big software packages would further add to that.
2) Snapshots. If you have more than 1 snapshot, then deleting snapshots will burn through P/E cycles, as will moving from one snapshot branch to another. If you only keep 1 snapshot at a time, then taking snapshots will hurt.
3) Pausing the VM. Each pause is either a hibernate or a snapshot, depending on the VM software.

As for whether or not it's worth it to put VMs on an SSD... Well, at the end of the day an SSD is a tool to be used, not an artistic masterpiece that needs to be preserved for hundreds of years in a temperature-controlled museum display. Why get an SSD if you're not going to be using it?

 

ssd write issue is not an issue, it's a myth spread on the web to have a reason to not yet having bought one.

put your vm's on it and be impressed how multiple os can run in parallel without slowing down the system.

don't bother about writes.

 

Sounds like a plan to me, Dave I am totally enjoying my 320 Intel 160GB and never think about writes.

 

While I can agree its a myth for most people's usage models and I agree to just use it till it dies, it is not a myth per se. These are basically limited write storage devices (compared to mechanical HDD's) and everyone knows that they can and do wear out. Especially the manufacturers - that is why they keep pushing the fact that an 'average' user can keep using them for a decade or more.

This is also the reason the new 710 Intel Series have new tech/nand that offers up to 65x the writes of current MLC nand chips (they use MLC-HET nand). For the truly enterprise users, SLC is still superior though, offering almost 28x more write endurance than MLC-HET technology gives.

Combined, that is about 2800x the endurance of today's commonly available MLC nand based SSD's. Now, we're talking.

See:
AnandTech - Intel SSD 710 and 720 Series Specifications Revealed

 

hdds are limited write storage devices, too. you just don't know when they die.

humans are limited, too. we all die. does that mean we have to care about everything and calculate towards our estimated end of life all the time?

no.

even with much usage, an ssd lasts long enough to not matter. thus, it's a myth, nothing more. the myth is, that it DOES matter, that one HAS to take special care all the time, and think about what writes and all. this is not true.

and the OTHER myth is, that caring about writes have any non-diminishing impact on the overall writes. people don't know well about writes anyways. "i download much. should i download to the hdd, and then copy over??". yeah, as if that would CHANGE ANYTHING?!

etc..

those drives last long enough that any manual change in behaviour will not have a noticable impact. ergo this is a myth.

write-prevention does not matter.

everything dies at some point. it's a myth to believe that this is anything to special consider on an ssd. it's a myth to consider this a flaw. it's a myth to think it's important.
EVERYTHING dies.

so prepare for death, and do backups. that's all.

it's like toystory 2: do you want to be played with, or do you want to be a perfect toy for ever, but no one ever takes you out of the box?

don't care about an ssd. it's there to be used AND abused.

 

Guys I'm not specifically talking about "wear" in the sense that the SSD will die (no more write allowed). I mean if you write too much on it the perfs will go down. OK TRIM is there to help but one thing I'm not sure is what happen when you virtualize an OS that does not support TRIM?? Is it still OK (because the host will be Win7) or can it be a problem? As far as I know the linux kernel now supports TRIM but...

Not to mention that VM's take a lot of storage space, hence filling up the precious SSD space, hence decreasing the perfs etc. In such usage I wonder whether using an mSata SSD for Win7 and installing VMs on an additional HDD in the 2.5" bay of my laptop would be better. I'm planning to install one VM with Win7 (as a test environment) + another VM with Ubuntu.... My initial thought was to get a 128Gb SATAIII SSD or the 160Gb intel 320 but I cannot afford a 256Gb SSD. An intel 310 80Gb + 320Gb HDD may be another option...

 

Ah, that make sense. guest OS would not pass on TRIM. It is the hosting OS that handle TRIM(and it doesn't know what the guest is doing).

A simple remedy would be to periodically copy the VHD to another location, delete the original one then put it back to where it is(done on the hosting OS). This would incurr some extra sequential write but would give the SSD a chance to clean the house.

Though I never worry about the 'no TRIM' case for my VM usage. SSD is for me to use(and enhance my productivity), not to TLC.

 

The 7 series are designed specifically for 'hot data' and not for general purpose use.

BTW, this line in anandtech's article is interesting
OCZ has pretty much been the dominator of PCIe SSD market but Intel's 720 Series could offer some serious competition in the high-end PCIe SSD market.

Sure there are lots of PCIe model from OCZ but dominator ? I am not sure if he has ever heard about Fusion-io and the like. What enterprise in their right mind would use OCZ product ?