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averylarry2
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First write to datastorage shows half throughput

ESXi 4 Promise SAN. Created 80Gb virtual disk (not thin-provisioned). Guest is SUSE 10.2.

Simply using dd if=/dev/zero of=/test.txt

In performance under Disk, the host performance shows ~75Mb/s write while the guest performance shows 37.5Mb/s (this is in the VSphere client's performance charts). The guest console shows about 40Mb/s.

Now if I delete that file and run the exact same test, it'll run at ~110Mb/s on both the host, guest, and guest console UNTIL it hits the same file size that the file I deleted was and then it goes back to the 75Mb/s -- 37.5Mb/s oddity.

I finally let it write the entire disk. I then deleted the file and rebooted the ESXi server. Everything ran at ~110Mb/s.

Any explanation? The SAN enclosure was fully synchronized. I thought it might have something to do with writing zeros the whole timebut that wouldn't explain the discrepancy between the host performance chart and the guest performance chartso I wrote some actual data (thousands of small files) to the drive, deleted that, and tried again with the ~110Mb/s performance.

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