Your questions help me to digg deeper on this. I've never really use ESXTOP but that's the good point, %VMwait is very high with Linked clone disk.Why?
I did more tests but this time on completely isolated environment: non-production ESXi server, new VmWare View plateform (vCenter, composer, connection server). The share datastore is on isolated SAN, without others connections on it.
I used this IOmeter config (below I've attached the completed config):
'size,% of size,% reads,% random,delay,burst,align,reply
| 4096,100,20,100,0,1,4096,0 |
The results are identical: the Linked clone disk is really slower and the metric %VMwait is very high. There is something under the hood about Linked clone mecanism that slow the I/O transfer. The problem comes from writes I/O, not read. There is something happenning when the Linked clone VM writes to disk. For sure the I/O can't go on the read-only replica so the write is redirected to "delta" disk and this seems to consume a lot of resource. Or I misonderstood the results?
I've attached the results. Just to compare and to exlude SAN iSCSI component, I did the same test on the local store. The same happen: linked clone are very slow at the moment writes are commited.
share_store_LINKED_VDI_IO_test.png
![share_store_LINKED_VDI_IO_test.png]()
share_store_NOT_LINKED_VDI_IO_test.png
![share_store_NOT_LINKED_VDI_IO_test.png]()
local_store_LINKED_VDI_IO_test.png
![local_store_LINKED_VDI_IO_test.png]()
Version 1.1.0
'TEST SETUP ====================================================================
'Test Description
'Run Time
' hours minutes seconds
0 0 0
'Ramp Up Time (s)
0
'Default Disk Workers to Spawn
NUMBER_OF_CPUS
'Default Network Workers to Spawn
0
'Record Results
ALL
'Worker Cycling
' start step step type
1 1 LINEAR
'Disk Cycling
' start step step type
1 1 LINEAR
'Queue Depth Cycling
' start end step step type
1 32 2 EXPONENTIAL
'Test Type
NORMAL
'END test setup
'RESULTS DISPLAY ===============================================================
'Record Last Update Results,Update Frequency,Update Type
DISABLED,1,WHOLE_TEST
'Bar chart 1 statistic
Total I/Os per Second
'Bar chart 2 statistic
Total MBs per Second (Decimal)
'Bar chart 3 statistic
Average I/O Response Time (ms)
'Bar chart 4 statistic
Maximum I/O Response Time (ms)
'Bar chart 5 statistic
% CPU Utilization (total)
'Bar chart 6 statistic
Total Error Count
'END results display
'ACCESS SPECIFICATIONS =========================================================
'Access specification name,default assignment
VDI,NONE
'size,% of size,% reads,% random,delay,burst,align,reply
4096,100,20,100,0,1,4096,0
'END access specifications
'MANAGER LIST ==================================================================
'Manager ID, manager name
1,XXX
'Manager network address
'Worker
Worker 1
'Worker type
DISK
'Default target settings for worker
'Number of outstanding IOs,test connection rate,transactions per connection,use fixed seed,fixed seed value
10,DISABLED,1,DISABLED,0
'Disk maximum size,starting sector,Data pattern
6144000,0,0
'End default target settings for worker
'Assigned access specs
'End assigned access specs
'Target assignments
'Target
C: "OS"
'Target type
DISK
'End target
'End target assignments
'End worker
'Worker
Worker 2
'Worker type
DISK
'Default target settings for worker
'Number of outstanding IOs,test connection rate,transactions per connection,use fixed seed,fixed seed value
1,DISABLED,1,DISABLED,0
'Disk maximum size,starting sector,Data pattern
0,0,0
'End default target settings for worker
'Assigned access specs
'End assigned access specs
'Target assignments
'End target assignments
'End worker
'End manager
'END manager list
Version 1.1.0
