Re: [gentoo-user] RAID-0 with LVM - is there any point?

[Bryan Whitehead]

I think you need to try running a real benchmark like bonnie++ against both.

For example, you run "time dd" but you don't include the "sync" in the 
time...

Daniel Iliev wrote:

>Neil Bothwick wrote:
>
>
>>Hello Daniel Iliev,
>>
>>
>>
>>
>>>Actually I'd be glad to read some results from a "Fake RAID-0 vs LVM"
>>>tests. My bet would be that RAID-0 w/o LVM would give the best speeds
>>>
>>>
>>>
>>Omitting LVM isn't an option, I'd lose all the flexibility that LVM
>>offers. I don't see why RAID-0 should be necessarily more efficient than
>>LVM, unless there's something superior about RAID-0's striping
>>algorithms. I could do some before and after tests, but I'd first have the
>>reformat the filesystems to remove any effects of fragmentation.
>>
>>If no one comes up with a good reason for keeping the RAID, I'll get rid
>>of it, running bonnie++ before and after.
>>
>>
>>
>>
>>
>
>Hi, Neil!
>
>Out of curiosity I made some tests which confirmed my expectations. What
>about you - did you have time (and wish) to take some performance
>benchmarks? I would be glad to see some additional results.
>
>I'm attaching my tests in file called "bench.txt".
>
>
>
>
>------------------------------------------------------------------------
>
>echo y | mdadm -C /dev/md9 -n2 /dev/sda11 /dev/sdb11 -l0
>mkfs.xfs /dev/md9
>mkdir /test
>mount /dev/md9 /test
>dd if=/dev/urandom of=/test.rnd bs=1M count=1500
>
>time cp /test.rnd /test
>real    0m44.981s
>user    0m0.036s
>sys     0m6.967s
>
>sync
>
>time mv /test.rnd /test
>real    0m47.514s
>user    0m0.047s
>sys     0m7.077s
>
>sync
>
>time mv /test/test.rnd /
>real    0m53.863s
>user    0m0.060s
>sys     0m8.885s
>
>mdadm --stop /dev/md9
>pvcreate /dev/sda11
>pvcreate /dev/sdb11
>vgcreate test /dev/sda11
>vgextend test /dev/sdb11
>vgdisplay | grep 'Total PE'
>  Total PE              1686
>lvcreate -i2 -l1686 -nlogvol test
>mkfs.xfs /dev/test/logvol
>mount /dev/test/logvol /test
>
>
>time cp /test.rnd /test
>
>real    1m12.183s
>user    0m0.039s
>sys     0m9.570s
>
>sync
>
>time mv /test.rnd /test
>
>real    0m51.643s
>user    0m0.044s
>sys     0m7.275s
>
>sync
>
>time mv /test/test.rnd /
>
>real    1m54.937s
>user    0m0.047s
>sys     0m9.556s
>
>
>=================
>BOTTOM LINE:
>
>cp /test.rnd /test
>LVM:        20.78 [MB/s]
>RAID-0:     33.41 [MB/s]
>
>mv /test.rnd /test
>LVM:        29.04[MB/s]
>RAID-0:     31.56[MB/s]
>
>mv /test/test.rnd /
>LVM:        11.11[MB/s]
>RAID-0:     27.84[MB/s]
>
>Strange: I repeated the last LVM test because it seemed to me as a low performance peak, but the result was again very low:
>time mv /test/test.rnd /
>
>real    1m27.775s
>user    0m0.050s
>sys     0m9.813s
>
>which is: 1500/87.775 = 17.089 [MB/s]
>
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