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List:       opensolaris-mktg
Subject:    [advocacy-discuss] RAMDISK performance
From:       Giovanni <g.lanaro () mindthegap ! it>
Date:       2010-05-24 21:47:37
Message-ID: 53714961.491274762887091.JavaMail.Twebapp () sf-app1
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Hello everybody, I think there might be performance issues with ramdisks (or I am \
missing something) and in general with disks

Test Environment: dual x5570 quad core, 32Gb ram ddr3 1333Mhz, supermicro board \
x8dthi, 16 600Gb SAS2 Cheetah 15K

First test: just create a 2Gb zerod file
time sh -c "dd if=/dev/zero of=/dev/null bs=8k count=308224"
real:0m0.315s
user:0m0.075s
sys:0m0.240s

This seems something less than 6GB/s

Second test: create a 2GB ramdisk and use it as a raw output (no filesystem on it)

ramdiskadm -a Test 2G
time sh -c "dd if=/dev/zero of=/dev/ramdisk/Test bs=8k count=308224"
real:0m3.433s
user:0m0.098s
sys:0m3.110s

What ? 2GB of zeros in more than 3 seconds ? This means 658MB/s


Then did the same test on a zpool raidz3 on the 16 disks

ramdiskadm -a Test 2G
time sh -c "dd if=/dev/zero of=/TestPool/Test bs=8k count=308224"
real:0m4.029s
user:0m0.125s
sys:0m3.541s

What ? 2GB of zeros on 16 disks which run at 200MB/s each at 578MB/s ?
ZIL is on another Cheetah, no cache disks

And, what is strange, disk performance is not far from ramdisk performance ?


Uh, what's on ? Anybody has got a clue here ?
Am I missing something ?
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