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Old 08-19-2012, 10:16 PM
"Smithies, Russell"
 
Default LVM overhead? Does it cripple I/O?

For a high-performance system (64-cores, 512GB RAM, 5TB local disk, 110TB NFS-mounted storage) is there any advantage of dropping lvm and mounting partitions directly?
We're not planning on changing partition sizes, but if we did we'd probably do a full rebuild.
Has anyone done performance testing to show that lvm isn't crippling I/O?

Thanx,

Russell

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Old 08-19-2012, 10:22 PM
Nux!
 
Default LVM overhead? Does it cripple I/O?

On 19.08.2012 23:16, Smithies, Russell wrote:
> For a high-performance system (64-cores, 512GB RAM, 5TB local disk,
> 110TB NFS-mounted storage) is there any advantage of dropping lvm and
> mounting partitions directly?
> We're not planning on changing partition sizes, but if we did we'd
> probably do a full rebuild.
> Has anyone done performance testing to show that lvm isn't crippling
> I/O?
>
> Thanx,
>
> Russell

I'm a long time user of LVM and I never noticed any problems with it,
let alone "crippling IO".
In some benchmarks[1] it even speeds up things and I believe the
Anaconda automatic partitioning defaults to LVM, too.

[1] -
http://www.phoronix.com/scan.php?page=article&item=fedora_15_lvm&num=3



--
Sent from the Delta quadrant using Borg technology!

Nux!
www.nux.ro
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Old 08-19-2012, 10:34 PM
John R Pierce
 
Default LVM overhead? Does it cripple I/O?

On 08/19/12 3:16 PM, Smithies, Russell wrote:
> For a high-performance system (64-cores, 512GB RAM, 5TB local disk, 110TB NFS-mounted storage) is there any advantage of dropping lvm and mounting partitions directly?
> We're not planning on changing partition sizes, but if we did we'd probably do a full rebuild.
> Has anyone done performance testing to show that lvm isn't crippling I/O?

running an extensive series of pgbench (postgresql benchmark similar to
tps-c) with and without lvm and using ext4 vs xfs, on a very large
raid10 built from 16 drives, the performance differences were pretty
much non-existant, down in the noise, less than 1%. this was on a 12
core (24 thread) 3Ghz 48GB ram system, using a LSI logic megasas2 raid
card with 512MB battery backed writeback cache. the IO in these tests
were 99% random write, and the tests were run with all 4 combinations of
LVM or not and EX4 vs XFS and with different client connection counts
(typically up around 100 client connections was where we got the peak
transaction throughput

the entire raid was dedicated to the database tests, the OS was running
on a seperate raid1 which had pretty much zero IO during the benchmark
sequences.

now, this isn't saying that you might not get a totally different result
under different test conditions.



--
john r pierce N 37, W 122
santa cruz ca mid-left coast

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