copy with "dd" command take long time when specifying block size

Hi,

make sure you are comparing apples with apples. Did the T4-4 use the same storage? Same disks with the same disk layout? Same filesystem with exactly the same mount options?

What happens to the run times if you leave out the "sync" command?

Andris

And when running this from within guest domains:

Is the storage attached the same way on both the T4-4 and the T5? How is it attached - does the domain access the storage directly or is the storage virtualized (vdisk or vhba)?

Are the control domains sized equally (CPU, RAM)?

Hi,

well, apples and oranges...

Unless your primary use case is to copy data with "dd", your comparison is useless.

I would bet that the vxfs has no mountoptions, which translates to "delaylog", meaning that you have a –3 second window where your data is not necessarily persistent. Try setting your mountoptions to "log,convosync=direct" and you'll see that your vxfs performance will drop dramatically.

Then, your workload is just small enough (800 MB resp 1,2GB) to fit into the STK 2540's cache. I don't know how large the cache for the FS1-2 is, but I guess that with larger workloads, the performance differences will level out.

The STK uses 15k RPM disks. How fast are the disks inside the FS1? Then, you don't mention how many disks make up your file systems.

The connection of the storage arrays also has different latencies. A direct connection should be slightly faster than a connection via a switch. Not much faster, but "100000 x not much faster" adds up.

Then on the topic of ZFS: What recordsize are you using? How is the zpool set up? Mirrored or Raid-Z-something? How full is the file system?

Andris

Hi.

For compare need select base. This can allow say that some feature or hardware is better or not.

You have whole different.

Different  servers, different arrays ( with different disks), different FS.

Any from this can be point of the problem.

You test:

root@T5_ldm_app:/# time sh -c " dd if=/dev/zero of=test.img bs=8k count=100000 && sync"

You copy 8k * 100 000 ~ 800 MB   Speed ~ 41 MB/s

root@T5_ldm_app:/# time sh -c " dd if=/dev/zero of=test.img bs=128k count=10000 && sync"

You copy 128k * 10 000  ~1280 MB Speed ~ 32 MB/s

But you sync all file systems. So it's not clear do you have any other activity on other file systems.

According  man:

     Unlike fsync(3C), which  completes  the  writing  before  it

     returns,  sync() schedules but does not necessarily complete

     the writing before returning.

So when you run only one sync, you can not be sure that buffers is real  flushed.

Regards,

Nik.