When I originally designed DPTPB Nutanix Dynamic shapes, I intentionally left out validity checks for disk sizes. This was done to save some time when making the shapes and reduce complexity in both using and making the shapes.
Supported disk sizes with NX appliances are changing over time, not just when a new hardware generation is released, but also with new AOS releases as more drives are qualified to be used with NX appliances. These changes in supported disk sizes should also be carried to the DPTPB Nutanix Dynamic shapes, by making updates to “disk size” lists and code associated with them.
This update requirement also meant that if I was lagging behind or skipping “disk size” updates, the shapes would slowly deteriorate and might be frustrating to use, especially if more stringent disk size usage rules or validity checks were in place. To give some freedom to end-users with the original dynamic shapes, there were no rules with mixing disk sizes, all supported disk sizes per platform were available to mix and match freely.
With disk size validity checks users might not be able to fully document environments if the Nutanix spec sheets were updated with new “disk usage rules” and the dynamic shapes lagged behind with updating this information.
But hold on.
Now that there is possibility to use custom disk sizes with the dynamic shapes, changes in supported disk sizes and updates to the dynamic shapes lagging behind would not be such a huge problem. Users could use custom “Generic” and “Manual Entry” disk sizes and get the drawing done with correct disk sizes while waiting for me to update the shapes. While not a perfect solution as you might end up with unsupported combination, but a feasible workaround.
Hmm, Maybe I should consider “disk size” validity checks again…
Three basic types of disk size rules
After studying the spec sheets I’ve identified three possible use cases where having “validity check” or “rules” for disk sizes might be useful to avoid generating drawings which would contain disk combinations that are not supported.
1: Mixing disk types limits the size of disks that can be used
Mostly found with NX platforms that support both hybrid configurations and 3.5″ drives.
One of the reasons behind this limitation is that you need a healthy amount of “hot” storage when compared to “cold” storage. “Hot” tier, usually SSD, serves as a destination for latency sensitive operations, while “cold” tier, usually HDD, is just a “graveyard” for cold data providing cheap capacity at higher (=worse) latency. If your “hot” tier is too small compared to your “cold” tier, you might not be able to serve your active workloads (or working sets) with acceptable latency level.
Obviously active data or active working set varies based on the workload, but it seems that Nutanix has decided to have a lower limit for this and is limiting using larger HDD drives with smaller SSD drives.
Sometimes similar limitations are found with NVMe+SSD hybrid configurations. While both SSD and NVMe are fast, NVMe is even “faster” and it might make sense to use these drives in healthy proportions.
Additionally there are some internal i/o components utilizing the “hot” tier. A certain base amount of “hot tier” is reserved to these internal i/o components, driving up the capacity requirement for “hot” tier.
2: With All Flash configurations supported SSD sizes are different than with Hybrid configurations (SSD+HDD or NVMe+SSD)
There are few variations of this kind of limitation to disk sizes
- All Flash supports all SSD sizes and Hybrid (SSD+HDD) only supports smaller SSD drives and the largest SSD drives are not supported with hybrid configurations
- All Flash supports all SSD sizes and Hybrid (SSD+HDD) only supports larger SSD drives and the smallest SSD drives are not supported with hybrid configurations
- All Flash supports smaller SSD sizes and with Hybrid configurations it is allowed to use larger SSD sizes
Some thoughts about these limits
- Most of the time the limits are quite logical and relate to keeping healthy ratio between different disk types
- There are differences between G6 and G7 generations of the same hw platform
- To me the limits with G7 are more logical
- While more relaxed limitations with G6 generation are sometimes confusing
- If a disk combination is allowed with G6
- how come it is not with G7?
- I will cover these irregularities in a future post
3: The disk size limits the number of drives
With all NX appliances there are upper limits how much capacity a given platform can support or is qualified for. In many cases this upper capacity limit is applied in the spec sheets by not allowing to use disk sizes which would exceed the upper capacity limit with fully populated nodes.
But then there are platforms, where the limit is done differently, by allowing certain disk sizes, but limiting the number of disks used.
So far I’ve identified only one NX model with this kind of limitation. With NX-8150-G7 it is supported to use 7.68TB SSD drives, but you are limited to use only 8x,12x,16x drives. It seems that using 20×7.68TB or 24×7.68TB drives with NX-8150-G7 would exceed the platform capacity limit.
You can fully populate NX-8150-G7 with 24xSSD drives when using smaller SSD drives.
Disk Size rules with Dynamic Shapes
The new rules regarding disk sizes are implemented by additional disk size lists and some code dynamically populating the pull-down menus with appropriate disk size lists based on your other selections in “Disk Layout” pull-down menu and in other “Disk XXX size” menus.
While it might sound complicated and it was somewhat complex to code, the good news for end-users is that it is not that complicated to use.
Most of the time the rules are invisible to end-users. Especially if you follow “top-to-bottom” workflow, i.e use top pull-down menu first and work you way down to bottom pull-down menu.
For example:
- By selecting a “Disk Layout” first
- the disk size pull-down menus are automatically populated with disk sizes compatible with your “Disk Layout” selection.
- As you move forward and select SSD size for your (hybrid) layout
- the available HDD sizes are automatically adjusted to your SSD size selection
- and likewise for other disk types
“Disk Size Rule” engine in action
If you don’t follow “top-to-bottom” workflow in some cases your disk size selection might be deselected because of “disk size rule” violation. In such case the built-in automation will repopulate the disk size menu for the offending disk type with supported disk sizes and users just have to reselect a disk size which is supported.
Example of “disk size rule” violation:
- “NX-8155-G7 Dyn (F)” shape used
- “2xSSD+10xHDD” selected as disk layout
- “SSD 3.84TB” selected as SSD size
- “HDD 12TB” selected as HDD size
- User goes back to “Select SSD Size” pull-down menu
- and selects “SSD 1.92TB” as new SSD size
- Because “HDD 12TB” is not supported with “SSD 1.92TB” when using NX-8155-G7
- “Disk size rule” engine kicks in
- “Select HDD Size” pull-down menu selection is deselected
- “Select HDD Size” pull-down menu is populated with HDD sizes that are compatible with “SSD 1.92TB” and NX-8155-G7
- User can now select one of the supported HDD sizes from “Select HDD Size” pull-down menu
- Available sizes “HDD 6TB” and “HDD 8TB”
Disk size rules with “Generic” and “Manual Entry” options
“Generic” and “Manual Entry” options for “Select Disk Sizes Used” pull-down menu were designed to offer a workaround in a situation where “Supported” disk size list does not contain desired disk size. As such it does not make much sense to apply “Disk Size Rules” when these menu options are in effect.
“Disk Size Rules” are only in use when “Supported” option is selected in “Select Disk Sizes Used” pull-down menu.
Example 1: NX-8155-G7 Hybrid with smaller SSD drives
Example 1.1: Starting point
- NX-8155-G7 Dyn (F) shape pulled to a drawing
- No selections in the shape data pull-down menus
- No disk labels
Example 1.2: Selection in “Select Disk Layout” pull-down menu
- A hybrid “2xSSD+10xHDD” disk layout selected
Example 1.3: resulting NX-8155-G7 shape based on selections above
- disk labels are color coded according to your selection
- Green = SSD
- Blue = HDD
Example 1.4: Selection of smaller SSD drive in “Select SSD Size” pull-down menu
- Based on your “Select Disk Layout” selection
- “Select SSD Size” pull-down menu is populated with disk sizes which are supported with selected disk layout
- “SSD 1.92TB” is selected
Example 1.5: resulting NX-8155-G7 shape based on selections above
- SSD drives are labeled with “SSD 1.92TB” based on your “Select SSD Size” selection
Example 1.6: NX-8155-G7 selection in “Select HDD” pull-down menu
- Based on your “Select Disk Layout” and “Select SSD Size” selection
- “Select HDD Size” pull-down menu is populated with disk sizes which are supported with selected disk layout & SSD size
- “HDD 8TB” is selected
Example 1.7: Final result NX-8155-G7 Hybrid based on selections above
- HDD drives are labeled with “HDD 8TB” based on your “Select HDD Size” selection
- No “Disk Size Rule” violations, none of the selections was deselected and “Disk Size Rule” engine was basically invisible to the end-user
Example 2: NX-8155-G7 Hybrid with larger SSD drives
Example 2.1: Starting point
- The same starting point as in the previous example
- NX-8155-G7 Dyn (F) shape pulled to a drawing
- No selections in the shape data pull-down menus
- No disk labels
Example 2.2: Selection in “Select Disk Layout” pull-down menu
- A hybrid “2xSSD+10xHDD” disk layout selected
- The same selection as in the previous example
Example 2.3: resulting NX-8155-G7 shape based on selections above
- disk labels are color coded according to your selection
- Green = SSD
- Blue = HDD
Example 2.4: Selection of larger SSD drive in “Select SSD” pull-down menu
- Based on your “Select Disk Layout” selection
- “Select SSD Size” pull-down menu is populated with disk sizes which are supported with selected disk layout
- this time a larger “SSD 3.84TB” is selected
Example 2.5: resulting NX-8155-G7 shape based on selections above
- SSD drives are labeled with “SSD 3.84TB” based on your “Select SSD Size” selection
Example 2.6: Selection in “Select HDD” pull-down menu
- Based on your “Select Disk Layout” and “Select SSD Size” selection
- The “Select HDD Size” pull-down menu is populated disk sizes compatible with previous selections
- Since we had chosen to use larger SSD drives, there are more sizes available for HDDs
- A previously unavailable “HDD 12TB” selected
Example 2.7: Final result NX-8155-G7 shape based on selections above
- HDD drives are labeled with “HDD 12TB” based on your “Select HDD Size” selection
- No “Disk Size Rule” violations, none of the user selections was deselected and “Disk Size Rule” engine was basically invisible to the end-user
Example 3: NX-8155-G7 Hybrid, changing to smaller SSD after HDD selection is made
Example 3.1: Starting point
- Starting point is the same setup where the previous example ended
- A Hybrid NX-8155-G7 with 2xSSD 3.84TB + 10xHDD 12TB
Example 3.2: (Re)Selection of smaller SSD drive in “Select SSD Size” pull-down menu
- SSD Size selection is changed from “SSD 3.84TB” to “SSD 1.92TB”
Example 3.3: resulting NX-8155-G7 shape based on selections above
- SSD drive are labeled with “SSD 1.92” based on your selection in “Select SSD Size” pull-down menu
- HDD drive labels are cleared as result of “Disk Size Rule” violation
Example 3.4: Selection of smaller HDD drive in “Select HDD Size” pull-down menu
- Your “SSD Size” selection caused a “Disk Size Rule” violation
- “HDD Size” selection pull-down menu was repopulated with supported HDD sizes
- “HDD 12TB” is not available anymore as it is unsupported to use it with “SSD 1.92TB”
- You previous selection is deselected automatically
- And new HDD size can be selected (“HDD 8TB”)
Example 3.5: Final result NX-8155-G7 shape based on selections above
- Because of “Disk Size Rule” violation previous HDD size selection was deselected and end-user had to (re)select one of the supported HDD sizes
Example 4: NX-8150-G7 All Flash with SSD drives
Example 4.1: Starting point
- “NX-8150-G7 Dyn (F) shape used
- “24xSSD” selected in “Shape Data” / “Select Disk Layout”
- “SSD 3.84TB” selected in “Shape Data” / “Select SSD Size”
Example 4.2: “Select SSD Size” pull-down menu
- The largest available SSD size is “SSD 3.84TB”
Example 4.3: “Select Disk Layout” pull-down menu, changing disk layout
- Disk layout selection is changed from “24xSSD” to “16xSSD”
Example 4.4: “Select SSD Size” pull-down menu, changing SSD size
- With lesser number of SSD drives, now “SSD 7.68TB” is also available (selected)
Example 4.5: Final result NX-8150-G7 shape based on selections above
- Originally your “Disk Layout” selection limited the available “SSD Sizes”
- Once “Disk Layout” was changed to “16xSSD”
- A new disk size “SSD 7.68TB” appeared in “Select SSD Size” pull-down menu
Downloads
Please visit the Nutanix stencil download page for the latest dynamic stencil package.
Since these are unofficial Visio shapes, they are not available on visiocafe.com, where the official stencil package resides.
Further documentation
- Intro
- Front & Rear View Shape usage
- Cables & Labels
- NX-1175S-G7 & NX-1175S-G6
- NX-1065-G7 /-G6 & NX-3060-G7 /-G6
- NX-8150-G7 & NX-8155-G7/ -G6 & NX-5155-G6
- NX-8035-G7 & NX-8035-G6
- NX-8170-G7 & NX-3170-G6
- NX-3155-G7 & NX-3155-G6
- Non-Dynamic mode
- Custom Disk Sizes
- Disk Size Validity Checks (this post)
- Why unofficial shapes?
- Limitations
- Update Notes
- NX-3170-G7 & Minor updates
- NX-8170-G7 with partially populated NVMe bays
- NX-1120S-G7 & Minor updates
DontPokeThePolarBear 