Hola, yo soy Elver Sena Sosa. And now
we're going to talk about failures to tolerate or FTT. In vSAN there is a
feature one of those SPBMS you can use that allows you to provide storage
redundancy to your VMs or your objects so that in case of a physical component
failure whether is the capacity this the cache drive or a host or a failure
domain the VM itself will continue to have access to that data because there
will be multiple copies of it or a way to get a recover the data from the
remaining host that are still running so we're going to do an example of how
we handle FTT equals to 1. Which means failure to tolerate equal to 1 so if one
physical opponent dies the VM will still have access to that component or that
the objects that what the components constitutes so in a case
among FTT equals to 1 when you enable that SPBM for a particular object
vSAN will automatically create multiple components of that VMDK or the object
in this case we're talking about VMDK. So in the case of entities equals to 1 we
have already the VMDK has already a component is being placed in this host
on this disk group now vSAN will go ahead and find a different host a
different disk group, in the different host, where to put a second component
which is called a replica. So in this case it can go here, here, here or here. So
let's choose this one. So these two components are for the same object and
they have the same information in this example and they're called a replica. So
when the VM executes a right to the VMDK the right goes to the ESXi base the
hypervisor witness realizes oh that's for vSAN
and causes the vSAN process to come and process this. And then, when the
vSAN process comes in and processes this they go, oh I see that there are two
replicas for this object so I need to send two right commands. One to the first
component or component number one and the second one over the network to the
second component which is in process by the vSAN recent current normal process in
that host. vSAN goes to the cache, the cache acknowledges. And this is a part
that is good to understand these two guys are both gonna acknowledge the
right of the block from the cache but let's say that this one arrives at the vSAN process on the source first.
The vSAN process here will not acknowledge
the right to the ESXi days the hypervisor until it receives
an acknowledgment back from the second component. Once both components
have acknowledged the right back to the source host the one running the
process over here then the ESXi base the hypervisor is told about it
who then tells the VM which is according to the VMDK knowing about this. In
this particular example we did at FTT equals to one but the method that
we use was to have a duplicate of the component two copies of it. This is using
a method of Raid 1. It's a mirror. Now, however, there is a slight problem
that we have right now and that is that because we have two of them it
is possible that within a network partition you can have these guys not seeing
each other and you can have a split brain situation so to fix that problem
vSAN institutes or creates a third component which is called the witness
and that third component needs to be placed in a failure domain or a
host that is different from the ones that already holding the two components.
So the witness will be placed either here, or here, or here. Let's select this
one
so this host would have a witness component which takes about four
megabytes of space on the disk group and that witness component - its job is to
keep track or the blocks that are written of the two replicas over here
and making sure that the two are in sync if this witness discovers that these two
are not in sync anymore vSAN would take steps to remediate find
out which of the two has the actual data and if needed copy data to the one that
is off sync. And with that we conclude the failure to tolerant
equals to 1. This is Elver Sena Sosa. Thank you for watching.