Sometimes we need to check that everything is working fine with SSD. In order to check that, first connect to esxi via ssh

~ # esxcli storage vflash cache list
vfc-1540989573-server.xxxxxxxx-000001

# esxcli storage vflash cache stats
Usage: esxcli storage vflash cache stats {cmd} [cmd options]

Available Commands:
get                   Get vflash cache statistics.
reset                 Reset vflash cache statistics.

 

In this case vfc-1540989573-server.xxxxxxxx-000001  is the virual machine id

Now we’ll use:
# esxcli storage vflash cache stats

# esxcli storage vflash cache stats get
Error: Missing required parameter -c|–cache-name

Usage: esxcli storage vflash cache stats get [cmd options]

Description:
get                   Get vflash cache statistics.

Cmd options:
-c|–cache-name=<str> The vflash cache file name (required)
-m|–module-name=<str>
The vflash module name

Now it’s time to run the complete  command to get all information related with Flash cache, so here the result.:

~ # esxcli storage vflash cache stats get -m vfc -c vfc-1540989573-server.xxxxxxxx-000001
Read:
Cache hit rate (as a percentage): 6
Total cache I/Os: 8068
Mean cache I/O latency (in microseconds): 288
Mean disk I/O latency (in microseconds): 20807
Total I/Os: 146717
Mean IOPS: 101
Max observed IOPS: 101
Mean number of KB per I/O: 2365
Max observed number of KB per I/O: 2365
Mean I/O latency (in microseconds): 9862
Max observed I/O latency (in microseconds): 9862
Evict:
Last I/O operation time (in microseconds): 0
Number of I/O blocks in last operation: 0
Mean blocks per I/O operation: 0
Total failed SSD I/Os: 0
Total failed disk I/Os: 0
Mean number of cache blocks in use: 265818

Once you know everything is working fine, Total I/Os: 146717 is the evidence that SSD is receiving I/O’s interactions.

The second and probably the most important thing you have to do is to get the specific block size for the virtual machine.

~ # vscsiStats -l

~ # vscsiStats -l
Virtual Machine worldGroupID: 495475, Virtual Machine Display Name: server.hostingred.com, Virtual Machine Config File: /vmfs/volumes/53479e2c-387086b8/server.hostingred.com/server.hostingred.com.vmx, {
Virtual SCSI Disk handleID: 8241 (scsi0:0)
Virtual SCSI Disk handleID: 8242 (scsi0:1)
Virtual SCSI Disk handleID: 8243 (scsi0:2)
}

And run the following  on a busy day at least 2 or 3 hours:

~ # vscsiStats -s -w 495475
vscsiStats: Starting Vscsi stats collection for worldGroup 495475, handleID 8241 (scsi0:0)
Success.
vscsiStats: Starting Vscsi stats collection for worldGroup 495475, handleID 8242 (scsi0:1)
Success.
vscsiStats: Starting Vscsi stats collection for worldGroup 495475, handleID 8243 (scsi0:2)
Success.

Where 495475 is the worldGroupID, so you have to check your own id, or ids in your infrastructure.

At the end, run :

~ # vscsiStats -p ioLength
Histogram: IO lengths of commands for virtual machine worldGroupID : 495475, virtual disk handleID : 8241 (scsi0:0) {
min : 4096
max : 524288
mean : 8980
count : 366944
{
0 (<= 512) 0 (<= 1024) 0 (<= 2048) 0 (<= 4095) 218406 (<= 4096) 0 (<= 8191) 47401 (<= 8192) 40948 (<= 16383) 52524 (<= 16384) 3251 (<= 32768) 1532 (<= 49152) 165 (<= 65535) 751 (<= 65536) 467 (<= 81920) 477 (<= 131072) 393 (<= 262144) 629 (<= 524288) 0 (> 524288)
}
}
Histogram: IO lengths of Read commands for virtual machine worldGroupID : 495475, virtual disk handleID : 8241 (scsi0:0) {
min : 4096
max : 262144
mean : 22133
count : 2442
{
0 (<= 512) 0 (<= 1024) 0 (<= 2048) 0 (<= 4095) 85 (<= 4096) 0 (<= 8191) 28 (<= 8192) 16 (<= 16383) 2018 (<= 16384) 144 (<= 32768) 36 (<= 49152) 2 (<= 65535) 27 (<= 65536) 15 (<= 81920) 45 (<= 131072) 26 (<= 262144) 0 (<= 524288) 0 (> 524288)
}
}
Histogram: IO lengths of Write commands for virtual machine worldGroupID : 495475, virtual disk handleID : 8241 (scsi0:0) {
min : 4096
max : 524288
mean : 8892
count : 364502
{
0 (<= 512) 0 (<= 1024) 0 (<= 2048) 0 (<= 4095) 218321 (<= 4096) 0 (<= 8191) 47373 (<= 8192) 40932 (<= 16383) 50506 (<= 16384) 3107 (<= 32768) 1496 (<= 49152) 163 (<= 65535) 724 (<= 65536) 452 (<= 81920) 432 (<= 131072) 367 (<= 262144) 629 (<= 524288) 0 (> 524288)
}
}
Histogram: IO lengths of commands for virtual machine worldGroupID : 495475, virtual disk handleID : 8242 (scsi0:1) {
min : 4096
max : 524288
mean : 22127
count : 4659
{
0 (<= 512) 0 (<= 1024) 0 (<= 2048) 0 (<= 4095) 2330 (<= 4096) 0 (<= 8191) 65 (<= 8192) 69 (<= 16383) 1612 (<= 16384) 224 (<= 32768) 80 (<= 49152) 5 (<= 65535) 40 (<= 65536) 29 (<= 81920) 37 (<= 131072) 101 (<= 262144) 67 (<= 524288) 0 (> 524288)
}
}
Histogram: IO lengths of Read commands for virtual machine worldGroupID : 495475, virtual disk handleID : 8242 (scsi0:1) {
min : 4096
max : 262144
mean : 27578
count : 1232
{
0 (<= 512) 0 (<= 1024) 0 (<= 2048) 0 (<= 4095) 18 (<= 4096) 0 (<= 8191) 3 (<= 8192) 2 (<= 16383) 1023 (<= 16384) 54 (<= 32768) 24 (<= 49152) 0 (<= 65535) 25 (<= 65536) 14 (<= 81920) 23 (<= 131072) 46 (<= 262144) 0 (<= 524288) 0 (> 524288)
}
}
Histogram: IO lengths of Write commands for virtual machine worldGroupID : 495475, virtual disk handleID : 8242 (scsi0:1) {
min : 4096
max : 524288
mean : 20168
count : 3427
{
0 (<= 512) 0 (<= 1024) 0 (<= 2048) 0 (<= 4095) 2312 (<= 4096) 0 (<= 8191) 62 (<= 8192) 67 (<= 16383) 589 (<= 16384) 170 (<= 32768) 56 (<= 49152) 5 (<= 65535) 15 (<= 65536) 15 (<= 81920) 14 (<= 131072) 55 (<= 262144) 67 (<= 524288) 0 (> 524288)
}
}
Histogram: IO lengths of commands for virtual machine worldGroupID : 495475, virtual disk handleID : 8243 (scsi0:2) {
min : 4096
max : 524288
mean : 19174
count : 4374
{
0 (<= 512) 0 (<= 1024) 0 (<= 2048) 0 (<= 4095) 1806 (<= 4096) 0 (<= 8191) 20 (<= 8192) 131 (<= 16383) 1851 (<= 16384) 220 (<= 32768) 128 (<= 49152) 34 (<= 65535) 37 (<= 65536) 36 (<= 81920) 50 (<= 131072) 31 (<= 262144) 30 (<= 524288) 0 (> 524288)
}
}
Histogram: IO lengths of Read commands for virtual machine worldGroupID : 495475, virtual disk handleID : 8243 (scsi0:2) {
min : 4096
max : 262144
mean : 26251
count : 758
{
0 (<= 512) 0 (<= 1024) 0 (<= 2048) 0 (<= 4095) 87 (<= 4096) 0 (<= 8191) 0 (<= 8192) 5 (<= 16383) 534 (<= 16384) ---ESTABLISH THIS VALUE 40 (<= 32768) 21 (<= 49152) 0 (<= 65535) 13 (<= 65536) 13 (<= 81920) 30 (<= 131072) 15 (<= 262144) 0 (<= 524288) 0 (> 524288)
}
}
Histogram: IO lengths of Write commands for virtual machine worldGroupID : 495475, virtual disk handleID : 8243 (scsi0:2) {
min : 4096
max : 524288
mean : 17691
count : 3616
{
0 (<= 512) 0 (<= 1024) 0 (<= 2048) 0 (<= 4095) 1719 (<= 4096) 0 (<= 8191) 20 (<= 8192) 126 (<= 16383) 1317 (<= 16384) 180 (<= 32768) 107 (<= 49152) 34 (<= 65535) 24 (<= 65536) 23 (<= 81920) 20 (<= 131072) 16 (<= 262144) 30 (<= 524288) 0 (> 524288)
}
}

Specifically you need to look for this section : IO lengths of Read commands

And now establish the value:

Anderson Alfaro

I am passionate for knowledge of Cloud technologies and reading the Bible as both make sense to me, but this last one keeps me on the ground and not in the cloud. Prov 16:18
VCP - MCSA - MCTS - RHCSA - RHCE - RHCVA

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