compare memory performance of two machines (low buffers vs high cached)
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I'm trying to compare the performance of two machines that I have. I have in both of the machines a database that was installed with the same settings. Both of the machines have the same amount of cpu(20Cores)/memory(65GB). Each machine is a vm in a dedicated esx with local disks.
I'm running the same operation in both of the machines but the results that I see in machine2 are far better then machine1 even though the hardware is the same. I was trying to find the root cause and I started from investigating the memory. I watched on the output of free -m on both of the machines and I saw that during the entire operation the buffers/shared/cached have very different values :
machine 1(avg) used - 42GB, buffers - 450MB, shared - 1.9GB, cached - 39GB
machine 2 (avg) used-58GB, buffers - 2.8GB, shared - 4GB, cached - 29GB,
From what I understood cached means that data that is recently read from disk will be saved in cache to save I/O which means that in machine1 reads should be faster because cached col is bigger(In contrary to my results).
Any idea what can explain the results ? What else can I investigate ?
linux memory performance
asked Dec 16 at 17:32
JeyJ
10412
add a comment |
I'm trying to compare the performance of two machines that I have. I have in both of the machines a database that was installed with the same settings. Both of the machines have the same amount of cpu(20Cores)/memory(65GB). Each machine is a vm in a dedicated esx with local disks.
I'm running the same operation in both of the machines but the results that I see in machine2 are far better then machine1 even though the hardware is the same. I was trying to find the root cause and I started from investigating the memory. I watched on the output of free -m on both of the machines and I saw that during the entire operation the buffers/shared/cached have very different values :
machine 1(avg) used - 42GB, buffers - 450MB, shared - 1.9GB, cached - 39GB
machine 2 (avg) used-58GB, buffers - 2.8GB, shared - 4GB, cached - 29GB,
From what I understood cached means that data that is recently read from disk will be saved in cache to save I/O which means that in machine1 reads should be faster because cached col is bigger(In contrary to my results).
Any idea what can explain the results ? What else can I investigate ?
linux memory performance
asked Dec 16 at 17:32
JeyJ
10412
add a comment |
I'm trying to compare the performance of two machines that I have. I have in both of the machines a database that was installed with the same settings. Both of the machines have the same amount of cpu(20Cores)/memory(65GB). Each machine is a vm in a dedicated esx with local disks.
I'm running the same operation in both of the machines but the results that I see in machine2 are far better then machine1 even though the hardware is the same. I was trying to find the root cause and I started from investigating the memory. I watched on the output of free -m on both of the machines and I saw that during the entire operation the buffers/shared/cached have very different values :
machine 1(avg) used - 42GB, buffers - 450MB, shared - 1.9GB, cached - 39GB
machine 2 (avg) used-58GB, buffers - 2.8GB, shared - 4GB, cached - 29GB,
From what I understood cached means that data that is recently read from disk will be saved in cache to save I/O which means that in machine1 reads should be faster because cached col is bigger(In contrary to my results).
Any idea what can explain the results ? What else can I investigate ?
linux memory performance
asked Dec 16 at 17:32
JeyJ
10412
I'm trying to compare the performance of two machines that I have. I have in both of the machines a database that was installed with the same settings. Both of the machines have the same amount of cpu(20Cores)/memory(65GB). Each machine is a vm in a dedicated esx with local disks.
I'm running the same operation in both of the machines but the results that I see in machine2 are far better then machine1 even though the hardware is the same. I was trying to find the root cause and I started from investigating the memory. I watched on the output of free -m on both of the machines and I saw that during the entire operation the buffers/shared/cached have very different values :
machine 1(avg) used - 42GB, buffers - 450MB, shared - 1.9GB, cached - 39GB
machine 2 (avg) used-58GB, buffers - 2.8GB, shared - 4GB, cached - 29GB,
From what I understood cached means that data that is recently read from disk will be saved in cache to save I/O which means that in machine1 reads should be faster because cached col is bigger(In contrary to my results).
Any idea what can explain the results ? What else can I investigate ?
linux memory performance
linux memory performance
asked Dec 16 at 17:32
JeyJ
10412
asked Dec 16 at 17:32
JeyJ
10412
asked Dec 16 at 17:32
JeyJ
10412
asked Dec 16 at 17:32
JeyJ
10412
asked Dec 16 at 17:32
JeyJ
10412
10412
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
You can't compare the machines so easily. You need to address several points:
- The same disks (in sense of speed, I/O ops, cache, disk partitioning) on host systems and VMs. With the same configurations, LVM, etc.
- Same software - you should run the same version of host OS, same
patches, same settings - Same VMs - this is most important in your case because every virtual
machine will have a unique load. - Moreover same VM can show different kind of load depending on time of
day, operations running on this machine and so on
answered Dec 16 at 18:09
Romeo Ninov
5,20231827
I didnt mention it but both of the vms were created dedicated for my test so I'm sure that only my operations are running there. Both of the vms have the same os version.
– JeyJ
Dec 17 at 7:57
@JeyJ, the data for cache, buffers, etc is from VMs or from host machines?
– Romeo Ninov
Dec 17 at 8:03
all the data is from the Vms
– JeyJ
Dec 17 at 8:41
@JeyJ, do you have any other VMs on those hosts?
– Romeo Ninov
Dec 17 at 8:46
nope, each vm is alone in the esx.
– JeyJ
Dec 17 at 9:11
|
show 2 more comments
2.8GB of buffers is quite a lot. This almost certainly means that something does raw I/O on the block devices or bypasses the filesystem cache. This in turn means that either the drivers or whatever you're running on them is not the exact same.
- Compare the version of the software that you are running and its configuration
- Compare the kernel versions
- Compare the hardware emulation of the VMs on the ESX part
- May be worth comparing the actual hardware they are running on
- May be worth comparing the kernels on the hosts and the ESX version
answered Dec 16 at 19:17
V13
2,799613
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
You can't compare the machines so easily. You need to address several points:
- The same disks (in sense of speed, I/O ops, cache, disk partitioning) on host systems and VMs. With the same configurations, LVM, etc.
- Same software - you should run the same version of host OS, same
patches, same settings - Same VMs - this is most important in your case because every virtual
machine will have a unique load. - Moreover same VM can show different kind of load depending on time of
day, operations running on this machine and so on
answered Dec 16 at 18:09
Romeo Ninov
5,20231827
I didnt mention it but both of the vms were created dedicated for my test so I'm sure that only my operations are running there. Both of the vms have the same os version.
– JeyJ
Dec 17 at 7:57
@JeyJ, the data for cache, buffers, etc is from VMs or from host machines?
– Romeo Ninov
Dec 17 at 8:03
all the data is from the Vms
– JeyJ
Dec 17 at 8:41
@JeyJ, do you have any other VMs on those hosts?
– Romeo Ninov
Dec 17 at 8:46
nope, each vm is alone in the esx.
– JeyJ
Dec 17 at 9:11
|
show 2 more comments
You can't compare the machines so easily. You need to address several points:
- The same disks (in sense of speed, I/O ops, cache, disk partitioning) on host systems and VMs. With the same configurations, LVM, etc.
- Same software - you should run the same version of host OS, same
patches, same settings - Same VMs - this is most important in your case because every virtual
machine will have a unique load. - Moreover same VM can show different kind of load depending on time of
day, operations running on this machine and so on
answered Dec 16 at 18:09
Romeo Ninov
5,20231827
I didnt mention it but both of the vms were created dedicated for my test so I'm sure that only my operations are running there. Both of the vms have the same os version.
– JeyJ
Dec 17 at 7:57
@JeyJ, the data for cache, buffers, etc is from VMs or from host machines?
– Romeo Ninov
Dec 17 at 8:03
all the data is from the Vms
– JeyJ
Dec 17 at 8:41
@JeyJ, do you have any other VMs on those hosts?
– Romeo Ninov
Dec 17 at 8:46
nope, each vm is alone in the esx.
– JeyJ
Dec 17 at 9:11
|
show 2 more comments
You can't compare the machines so easily. You need to address several points:
- The same disks (in sense of speed, I/O ops, cache, disk partitioning) on host systems and VMs. With the same configurations, LVM, etc.
- Same software - you should run the same version of host OS, same
patches, same settings - Same VMs - this is most important in your case because every virtual
machine will have a unique load. - Moreover same VM can show different kind of load depending on time of
day, operations running on this machine and so on
answered Dec 16 at 18:09
Romeo Ninov
5,20231827
You can't compare the machines so easily. You need to address several points:
- The same disks (in sense of speed, I/O ops, cache, disk partitioning) on host systems and VMs. With the same configurations, LVM, etc.
- Same software - you should run the same version of host OS, same
patches, same settings - Same VMs - this is most important in your case because every virtual
machine will have a unique load. - Moreover same VM can show different kind of load depending on time of
day, operations running on this machine and so on
answered Dec 16 at 18:09
Romeo Ninov
5,20231827
edited Dec 17 at 9:14
answered Dec 16 at 18:09
Romeo Ninov
5,20231827
answered Dec 16 at 18:09
Romeo Ninov
5,20231827
answered Dec 16 at 18:09
Romeo Ninov
5,20231827
5,20231827
I didnt mention it but both of the vms were created dedicated for my test so I'm sure that only my operations are running there. Both of the vms have the same os version.
– JeyJ
Dec 17 at 7:57
@JeyJ, the data for cache, buffers, etc is from VMs or from host machines?
– Romeo Ninov
Dec 17 at 8:03
all the data is from the Vms
– JeyJ
Dec 17 at 8:41
@JeyJ, do you have any other VMs on those hosts?
– Romeo Ninov
Dec 17 at 8:46
nope, each vm is alone in the esx.
– JeyJ
Dec 17 at 9:11
|
show 2 more comments
I didnt mention it but both of the vms were created dedicated for my test so I'm sure that only my operations are running there. Both of the vms have the same os version.
– JeyJ
Dec 17 at 7:57
@JeyJ, the data for cache, buffers, etc is from VMs or from host machines?
– Romeo Ninov
Dec 17 at 8:03
all the data is from the Vms
– JeyJ
Dec 17 at 8:41
@JeyJ, do you have any other VMs on those hosts?
– Romeo Ninov
Dec 17 at 8:46
nope, each vm is alone in the esx.
– JeyJ
Dec 17 at 9:11
I didnt mention it but both of the vms were created dedicated for my test so I'm sure that only my operations are running there. Both of the vms have the same os version.
– JeyJ
Dec 17 at 7:57
I didnt mention it but both of the vms were created dedicated for my test so I'm sure that only my operations are running there. Both of the vms have the same os version.
– JeyJ
Dec 17 at 7:57
@JeyJ, the data for cache, buffers, etc is from VMs or from host machines?
– Romeo Ninov
Dec 17 at 8:03
@JeyJ, the data for cache, buffers, etc is from VMs or from host machines?
– Romeo Ninov
Dec 17 at 8:03
all the data is from the Vms
– JeyJ
Dec 17 at 8:41
all the data is from the Vms
– JeyJ
Dec 17 at 8:41
@JeyJ, do you have any other VMs on those hosts?
– Romeo Ninov
Dec 17 at 8:46
@JeyJ, do you have any other VMs on those hosts?
– Romeo Ninov
Dec 17 at 8:46
nope, each vm is alone in the esx.
– JeyJ
Dec 17 at 9:11
nope, each vm is alone in the esx.
– JeyJ
Dec 17 at 9:11
|
show 2 more comments
2.8GB of buffers is quite a lot. This almost certainly means that something does raw I/O on the block devices or bypasses the filesystem cache. This in turn means that either the drivers or whatever you're running on them is not the exact same.
- Compare the version of the software that you are running and its configuration
- Compare the kernel versions
- Compare the hardware emulation of the VMs on the ESX part
- May be worth comparing the actual hardware they are running on
- May be worth comparing the kernels on the hosts and the ESX version
answered Dec 16 at 19:17
V13
2,799613
add a comment |
2.8GB of buffers is quite a lot. This almost certainly means that something does raw I/O on the block devices or bypasses the filesystem cache. This in turn means that either the drivers or whatever you're running on them is not the exact same.
- Compare the version of the software that you are running and its configuration
- Compare the kernel versions
- Compare the hardware emulation of the VMs on the ESX part
- May be worth comparing the actual hardware they are running on
- May be worth comparing the kernels on the hosts and the ESX version
answered Dec 16 at 19:17
V13
2,799613
add a comment |
2.8GB of buffers is quite a lot. This almost certainly means that something does raw I/O on the block devices or bypasses the filesystem cache. This in turn means that either the drivers or whatever you're running on them is not the exact same.
- Compare the version of the software that you are running and its configuration
- Compare the kernel versions
- Compare the hardware emulation of the VMs on the ESX part
- May be worth comparing the actual hardware they are running on
- May be worth comparing the kernels on the hosts and the ESX version
answered Dec 16 at 19:17
V13
2,799613
2.8GB of buffers is quite a lot. This almost certainly means that something does raw I/O on the block devices or bypasses the filesystem cache. This in turn means that either the drivers or whatever you're running on them is not the exact same.
- Compare the version of the software that you are running and its configuration
- Compare the kernel versions
- Compare the hardware emulation of the VMs on the ESX part
- May be worth comparing the actual hardware they are running on
- May be worth comparing the kernels on the hosts and the ESX version
answered Dec 16 at 19:17
V13
2,799613
answered Dec 16 at 19:17
V13
2,799613
answered Dec 16 at 19:17
V13
2,799613
answered Dec 16 at 19:17
V13
2,799613
2,799613
add a comment |
add a comment |
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