Tag Archives: cluster

Sizing for your workloads

When sizing a vSAN environment there are many considerations to take into account, and with the launch of the new vSAN Sizing tool I thought I would take time and write up what questions I commonly ask people in order to get an understanding of what they want to run on vSAN as well as a scope of requirements that meet that workload.

Capacity
Obviously capacity is going to be our baseline for any sizing activity, no matter what we achieve with the other requirements, we have to meet a usable capacity, remember we should always work off a usable capacity for any sizing, a RAW capacity does not take into account any Failure Tolerance Methodology, Erasure Coding or Dedupe/Compression, this is something we will cover a bit later in this article.

Capacity should also include the required Swap File space for each of the VMs that the environment is being scoped for.

IOPS
I have been involved in many discussions where it is totally unknown what the performance requirements are going to be, so many times I have been told “We want the fastest performance possible” without being told what the current IOPS requirement is, to put it into context what is the point in buying a 200mph sports car when the requirement is to drive at 70mph max!

IOPS requirement plays a key part in determining what level of vSAN Ready Node specification is required, for example if a total IOPS requirement is 300,000 IOPS out of a 10 Node cluster, is there much point spending more money on an All-Flash configuration that delivers 150,000 IOPS Per node?  Simple answer…No!  You could opt for a lower vSAN All-Flash Ready Node config that meets the requirements a lot closer and still offer
room for expansion in the future.

Workload Type
This is a pretty important requirement, for example if your workload is more of a write intensive workload then this would change the cache requirements, it may also require a more write intensive flash technology such as NVMe for example.  If you have different workload types going onto the same cluster it would be worthwhile categorizing those workloads into four categories:-

  • 70/30 Read/Write
  • 80/20 Read/Write
  • 90/10 Read/Write
  • 50/50 Read/Write

Having the VMs in categories will allow you to specify the workload types in the sizing tool (in the advanced options).

vCPU to Physical Core count
This is something that gets overlooked not from a requirement perspective, but people are so used to sizing based on a “VM Per Host” scenario which with the increasing CPU core counts does not fit that model any more, even the new sizing tool bases it on vCPU to Physical Core ratio which makes things a lot easier, most customers I Talk to who are performing a refresh of servers with either 12 or 14 core processors can lower the amount of servers required by increasing the core count on the new servers, thus allowing you to run more vCPUs on a single host.

List of questions for requirements for each workload type

  • Average VMDK Size per VM
  • Average number of VMDKs per VM
  • Average number of vCPU per VM
  • Average vRAM per VM
  • Average IOPS Requirement per VM
  • Number of VMs
  • vCPU to Physical Core Ratio

RAW Capacity versus Usable Capacity, how much do I actually need?
The new sizing tool takes all your requirements into account, even the RAID levels, Dedupe/Compression ratios etc and returns with a RAW Capacity requirement based on the data you enter, if you are like me and prefer to do it quick and dirty, below is table showing you how to work out based on a requirement of 100TB of usable (Including Swap File Space), based on a standard cluster with no stretched capacilities it looks like this:

FTT LevelFTT MethodMin number of hostsMultiplication FactorRAW Capacity Based on 100TB Usable
FTT=0NoneN/A1x100TB
FTT=1Mirror32x200TB
FTT=2Mirror53x300TB
FTT=3Mirror74x400TB
FTT=1RAID541.33x133TB
FTT=2RAID661.5x150TB

Now in vSAN 6.6 VMware introduced localized protection (Secondary FTT) and the ability to include or not include specific objects from the stretched cluster (Primary FTT), below is a table showing what the RAW Capacity requirements are based on the two FTT levels

Primary FTT LevelSecondary FTT LevelFTT MethodMin Number of hosts per siteRAW Capacity Based on 100TB Usable
PFTT=1SFTT=1Mirror2400TB
PFTT=1SFTT=1RAID54266TB
PFTT=2SFTT=2RAID66300TB

Mixed FTT levels and FTT Methods
Because vSAN is truly a Software Defined Storage Platform, this means that you can have a mixture of VMs/Objects with varying levels of protection and FTT Methods, for example for Read intensive workloads you may choose to have RAID 5 in the storage policy, and for more write intensive workloads a RAID 1 policy, they can all co-exist on the same vSAN Cluster/Datastore perfectly well, and the new sizing tool allows you to specify different Protection Levels and Methods for each workload type.

 

Cache Sizing

Since vSAN was released in 2014 there has been a bit of confusion as to how much cache should be sized for the cluster, this article is intended to clear that up and provide direction for both Hybrid and All-Flash configurations.? The reason there are differences in the recommendations is primarily because in Hybrid the cache is a Read Cache as well as a Write Buffer and in All-Flash it’s just serving as a Write Buffer, so the sizing is not a “one size fits all”.

Capacity Definitions:

  • RAW Capacity – This is the amount of capacity the vSAN Datastore will provide
  • Usable Capacity – This is the amount of capacity that can be provided based on the FTT level specified in storage policies
  • Provisioned / Deployed Capacity – This is the amount of space taken by objects before FTT is taken into account
  • Consumed Capacity – This is the amount of space that has been consumed by objects taking into account FTT, for example a 100GB Object with FTT=1 will consume 200GB of storage space

 

Hybrid Cache Sizing
In Hybrid the recommendation has always been 10% of Usable Capacity or Deployed capacity, if we have a 3-Node vSAN cluster, each host has two disk groups and each disk group has 7×1.2TB 10K SAS Drives, that means each host has 16.8TB of RAW Capacity and our 3-Node cluster has 50.4TB of RAW Capacity, based on the following FTT Values in our storage policy this means our total Usable Capacity is:

FTT=0 – 50.4TB
FTT=1 – 25.2TB
FTT=2 – 16.8TB
FTT=3 – 12.6TB

Based on the 10% rule our cache requirements are as follows:

FTT=0 – 5.4TB which equates to 1.8TB Per node which equates to 900GB Per Disk Group
FTT=1 – 2.52TB which equates to 0.84TB Per node which equates to 420GB Per Disk Group
FTT=2 – 1.68TB which equates to 0.56TB Per node which equates to 280GB Per Disk Group
FTT=3 – 1.26TB which equates to 0.42TB Per node which equates to 210GB Per Disk Group

The above sizing is all well and good if you are only using a single FTT method, however vSAN allows you to define policies with different FTT levels which means you can have objects on vSAN that have varying levels of protection, this makes sizing using the above method all the more difficult.

The best way to size the cache in a Hybrid cluster is to base it on your deployed or provisioned capacity, for example in the above RAW capacity of 50.4TB you may choose to have the following as an example

10 Objects based on FTT=0 of 500GB which totals 5TB of Provisioned Capacity and 5TB of Consumed Capacity
10 Objects based on FTT=1 of 500GB which totals 5TB of Provisioned Capacity and 10TB of Consumed Capacty
10 Objects based on FTT=2 of 500GB which totals 5TB of Provisioned Capacity and 15TB of Consumed Capacity
10 Objects based on FTT=3 of 500GB which totals 5TB of Provisioned Capacity and 20TB of Consumed Capacity

If you total up the above, our Provisioned Capacity is 20TB but our Consumed Capacity is 50TB, based on the Provisioned Capacity of 20TB, 10% of this is 2TB which equates to 0.67TB Per Node, or 333GB per Disk Group, this is how your cache in Hybrid should be sized.

All-Flash Cache Sizing
All flash has a lot more factors to consider, Erasure Coding, Dedupe and Compression and the fact that the cache is purely a Write Buffer so we have to take into account write endurance so the usual 10% sizing does not apply here.? In reality the typical 70% Read / 30% Write workload means that a lot of the requests are coming from the Capacity Tier which in this case is flash based anyway, so this means that the cache layer can be much smaller than it would have been in Hybrid for the same RAW capacity, however there is the write endurance factor to take into account.? We all know there is a write buffer limit in vSAN but that does not mean you should limit the size of the SSD drives based on that, the main reason is to increase the endurance of the drive, vSAN will cycle through all the cells on the drive irrelevant of the Write Buffer Limit.? VMware recently published a new sizing guide for All-Flash which is shown below

 

There we have it!

 

 

Creating a vSAN Cluster without a vCenter Server

I have been asked many times about creating a 3-node vSAN cluster without a vCenter server, the main reason for doing this is that you need to place your vCenter server onto the vSAN datastore but have no where to host the vCenter server until doing so.? The many customers I have spoken to are not aware that they can do this from the command line very easily.? In order to do this you must have installed ESXi 6.0 U2 and enabled SSH access to the host, there are a few steps in order to do this

  1. Configure the vSAN VMKernel Interface
  2. Create the vSAN Cluster
  3. Add the other nodes to the cluster
  4. Claim the disks

Step 1 – Create the VMKernel interface
In order for vSAN to function you need to create a VMKernel Interface on each host, this requires other dependencies such as a vSwitch and a Port Group, so performing this on all three hosts is a must so lets do it in this order, firstly lets create our vSwitch, since vSwitch0 exists for the management network we’ll create a vSwitch1

esxcli network vswitch standard add -v vSwitch1

Once our vSwitch1 is created we then need to add the physical uplinks to our switch, to help identify which uplinks to use we run the following command

esxcli network nic list

This should return details on all the physical network cards on the host for example:

Name??? PCI????????? Driver????? Link Speed????? Duplex MAC Address?????? MTU??? Description
vmnic0? 0000:01:00.0 ntg3??????? Up?? 1000Mbps?? Full?? 44:a8:42:29:fe:98 1500?? Broadcom Corporation NetXtreme BCM5720 Gigabit Ethernet
vmnic1? 0000:01:00.1 ntg3??????? Up?? 1000Mbps?? Full?? 44:a8:42:29:fe:99 1500?? Broadcom Corporation NetXtreme BCM5720 Gigabit Ethernet
vmnic2? 0000:02:00.0 ntg3??????? Down 0Mbps????? Half?? 44:a8:42:29:fe:9a 1500?? Broadcom Corporation NetXtreme BCM5720 Gigabit Ethernet
vmnic3? 0000:02:00.1 ntg3??????? Down 0Mbps????? Half?? 44:a8:42:29:fe:9b 1500?? Broadcom Corporation NetXtreme BCM5720 Gigabit Ethernet
vmnic4? 0000:82:00.0 ixgbe?????? Up?? 10000Mbps? Full?? a0:36:9f:78:94:cc 1500?? Intel Corporation Ethernet Controller 10 Gigabit X540-AT2
vmnic5? 0000:82:00.1 ixgbe?????? Up?? 10000Mbps? Full?? a0:36:9f:78:94:ce 1500?? Intel Corporation Ethernet Controller 10 Gigabit X540-AT2
vmnic6? 0000:04:00.0 ixgbe?????? Up?? 10000Mbps? Full?? a0:36:9f:78:94:c4 1500?? Intel Corporation Ethernet Controller 10 Gigabit X540-AT2
vmnic7? 0000:04:00.1 ixgbe?????? Up?? 10000Mbps? Full?? a0:36:9f:78:94:c6 1500?? Intel Corporation Ethernet Controller 10 Gigabit X540-AT2

For my cluster I am going to add vmnic5 to the vSwitch1 so for this I run the following command:

esxcli network vswitch standard uplink add -v vSwitch1 -u vmnic5

Now that we now have our uplink connected to vSwitch1 we need to configure a portGroup for vSAN, for this I am calling my portGroup name “vSAN”

esxcfg-vswitch -A vSAN vSwitch1

Now we need to create out VMKernel interface with an IP Address (192.168.100.1 for Host 1), Subnet Mask and assign it to the “vSAN” portGroup

esxcfg-vmknic -a -i 192.168.100.1 -n 255.255.255.0 -p vSAN

We validate our VMKernel Interface by running the following command:

[root@se-emea-vsan01:~] esxcfg-vmknic -l
Interface? Port Group/DVPort/Opaque Network??????? IP Family IP Address????????????????????????????? Netmask???????? Broadcast?????? MAC Address?????? MTU???? TSO MSS?? Enabled Type??????????????? NetStack
vmk0?????? Management Network????????????????????? IPv4????? 172.16.101.1??????????????????????????? 255.255.252.0?? 172.16.103.255? 44:a8:42:29:fe:98 1500??? 65535???? true??? STATIC????????????? defaultTcpipStack
vmk1?????? vSAN??????????????????????????????????? IPv4????? 192.168.100.1?????????????????????????? 255.255.255.0?? 192.168.100.255 00:50:56:6a:5d:06 1500??? 65535???? true??? STATIC????????????? defaultTcpipStack

In order to add the VMKernel interface to vSAN we need to run the following command:

esxcli vsan network ip add -i vmk1

Repeat the above steps on the two remaining hosts that you wish to participate in the cluster

Step 2 – Creating the cluster
Once we have all the VMKernel interfaces configured on all hosts, we now need to create a vSAN Cluster on the first host, to do this we run the following command

esxcli vsan cluster new

Once completed we can get our vSAN Cluster UUID by running the following command:

[root@se-emea-vsan01:~] esxcli vsan cluster get
Cluster Information
?? Enabled: true
?? Current Local Time: 2016-11-21T15:17:57Z
?? Local Node UUID: 582a29ea-cbfc-195e-f794-a0369f7894c4
?? Local Node Type: NORMAL
?? Local Node State: MASTER
?? Local Node Health State: HEALTHY
?? Sub-Cluster Master UUID: 582a2bba-0fd8-b45a-7460-a0369f749a0c
?? Sub-Cluster Backup UUID: 582a29ea-cbfc-195e-f794-a0369f7894c4
?? Sub-Cluster UUID: 52bca225-0520-fd68-46c4-5e7edca5dfbd
?? Sub-Cluster Membership Entry Revision: 6
?? Sub-Cluster Member Count: 1
?? Sub-Cluster Member UUIDs: 582a29ea-cbfc-195e-f794-a0369f7894c4
?? Sub-Cluster Membership UUID: d2dd2c58-da70-bbb9-9e1a-a0369f749a0c

Step 3 – Adding the other nodes to the cluster
From the remaining hosts run the following command adding them to the newly created cluster

esxcli vsan cluster join -u 52bca225-0520-fd68-46c4-5e7edca5dfbd

You can verify that the nodes have successfully joined the cluster by running the same command we ran earlier noting that the Sub-Cluster Member Count has increased to 3 and it also shows the other sub cluster UUID Members:

[root@se-emea-vsan01:~] esxcli vsan cluster get
Cluster Information
?? Enabled: true
?? Current Local Time: 2016-11-21T15:17:57Z
?? Local Node UUID: 582a29ea-cbfc-195e-f794-a0369f7894c4
?? Local Node Type: NORMAL
?? Local Node State: MASTER
?? Local Node Health State: HEALTHY
?? Sub-Cluster Master UUID: 582a2bba-0fd8-b45a-7460-a0369f749a0c
?? Sub-Cluster Backup UUID: 582a29ea-cbfc-195e-f794-a0369f7894c4
?? Sub-Cluster UUID: 52bca225-0520-fd68-46c4-5e7edca5dfbd
?? Sub-Cluster Membership Entry Revision: 6
?? Sub-Cluster Member Count: 3
?? Sub-Cluster Member UUIDs: 582a29ea-cbfc-195e-f794-a0369f7894c4, 582a2bf8-4e36-abbf-5318-a0369f7894d4, 582a2c3b-d104-b96d-d089-a0369f78946c
?? Sub-Cluster Membership UUID: d2dd2c58-da70-bbb9-9e1a-a0369f749a0c

Step 4 – Claim Disks
Our cluster is now created and we need to claim the disks in each node to be used by vSAN, in order to do this we first of all need to identify which disks are to be used by vSAN as a Cache Disk and as Capacity Disks, and obviously the number of disk groups, to show the disk information for the disks in the host run the following command:

esxcli storage core device list

This will produce an output similar to the following where we can identify the NAA ID for each device:

naa.500003965c8a48a4
?? Display Name: TOSHIBA Serial Attached SCSI Disk (naa.500003965c8a48a4)
?? Has Settable Display Name: true
?? Size: 381554
?? Device Type: Direct-Access
?? Multipath Plugin: NMP
?? Devfs Path: /vmfs/devices/disks/naa.500003965c8a48a4
?? Vendor: TOSHIBA
?? Model: PX02SMF040
?? Revision: A3AF
?? SCSI Level: 6
?? Is Pseudo: false
?? Status: on
?? Is RDM Capable: true
?? Is Local: true
?? Is Removable: false
?? Is SSD: true
?? Is VVOL PE: false
?? Is Offline: false
?? Is Perennially Reserved: false
?? Queue Full Sample Size: 0
?? Queue Full Threshold: 0
?? Thin Provisioning Status: yes
?? Attached Filters:
?? VAAI Status: unknown
?? Other UIDs: vml.0200000000500003965c8a48a450583032534d
?? Is Shared Clusterwide: false
?? Is Local SAS Device: true
?? Is SAS: true
?? Is USB: false
?? Is Boot USB Device: false
?? Is Boot Device: false
?? Device Max Queue Depth: 64
?? No of outstanding IOs with competing worlds: 32
?? Drive Type: physical
?? RAID Level: NA
?? Number of Physical Drives: 1
?? Protection Enabled: false
?? PI Activated: false
?? PI Type: 0
?? PI Protection Mask: NO PROTECTION
?? Supported Guard Types: NO GUARD SUPPORT
?? DIX Enabled: false
?? DIX Guard Type: NO GUARD SUPPORT
?? Emulated DIX/DIF Enabled: false

In my setup I want to create two disk groups per host consisting of 4 capacity devices plus my cache so to create one disk group I run the following command:

esxcli vsan storage add -s <naa for cache disk> -d <naa for capacity disk 1> -d <naa for capacity disk 2> -d <naa for capacity disk 3> -d <naa for capacity disk 4>

Once you have performed the above on each of your hosts, your vSAN cluster is deployed with storage and you can now deploy your vCenter appliance onto the vSAN datastore where then you can manage your vSAN License, Storage Policies, switch on vSAN Services such as iSCSI, health service and performance services as well as start to deploy virtual machines