This morning I read the post by Gabe on his blog about ESXi on USB devices here. Coincidentally I’m taking a look at the ESXi installation of the HP BL460c G7 using kickstart. The installation process is explained in this post. This HP BL460c G7 blade server has two types of media to install ESX I to : SD or SSD. In this post I’ll try to explain what problems I ran into and my take on VMware not supporting the installation on SD / USB.
No scripted install to USB / SD device
Before getting into details : scripted install to USB (or SD which ESXi sees as a USB device) isn’t supported by VMware. This KB article by VMware explicitly says that you can’t install ESXi via scripted install.
“You cannot use Scripted Install to install ESXi Installable to a USB device”
Question however is : Why is this not supported? It’s not a technical issue. You can install ESXi to a USB / SD device when you install ESXi manually. And with kickstart you should be able to pinpoint the installation device to the USB / SD device. So why doesn’t VMware support the installation via scripted install to the USB / SD device?
I can only guess for the reason why. Haven’t found the answer to that question anywhere and would love to know. The only thing I can do is guess. My opinion about it is that is has something to do with embedded ESXi vs. installed ESXi.
Since it’s not technical issue, it must have some other reason. Just think when it would be possible to kickstart your ESXi installation to a USB / SD device, it would practically make the ESXi embedded solution obsolete. You just buy your servers with a non-installed USB device / SD card and install your own version of ESXi onto the USB / SD disk via kickstart. No need anymore for a the vendor specific ESXi embedded version.
Also taking into account the fact that most vendors are moving away from the ESXi embedded solution (for example HP discontinued ESXi embedded) , makes you wonder even more : Why can’t I install ESXi to a USB / SD device?
Making a choice : SD vs. SSD
So why, if VMware doesn’t support it, do you want to install to an SD device. Most server vendors currently install a SD slot into their server for the purpose of installing an OS onto a SD card. This gives you an installation method besides installing onto SSD disks.
From a cost perspective this is a huge benefit. For example an SD card for the HP BL460c G7 will cost you about 80 euros. An SSD disk in that same server will cost about 800 euros. Which in my opinion is a big difference in price if you take into account that the underlying technology (flash) is basically the same.
But from a redundancy design point of view it would be better to use the SSD disk. You will be able to put them in a RAID configuration. Which would prevent a single-point-of-failure in the server in case one of the SSD disks fails. Most server vendors don’t have a solution to make SD redundant. The only solution I know is the Dell Internal Dual SD module. So basically it’s an advantage of SSD over SD when looking at redundancy.
But you can also question that when you ask yourself what failure rate is to be expected of flash disks (SD or SSD) versus traditional HD disk. In general flash disks are more stable then traditional disks. More risk probably comes from a bad batch of SD or SSD disks than from a SD / SSD disk failing due to a technical error.
Then again if ESXi hosts fail, you always have VMware High Availability (HA) to kick in and save the day.
The choice of SD vs. SSD comes down to the same old design mantra : It depends.
The choice should be made based on the requirements that your vSphere design has to meet. It is based on the down time your company is willing to except. If it’s not a problem for VMs to go down for a couple of minutes then SD can be your preferred solution. If availability is key then you should go for the RAID SSD solution. Availability will cost you money as always.
But back to reality. SD isn’t supported with scripted install. So I had no choice. SSD it’s going to be. I do however regret that I don’t have the option to choose. I would like to see VMware supporting the kickstart scripted install for ESXi so I do have the option to install on USB / SD via scripted install.