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I have nearly two identical servers, the only difference between the
two is the version of Linux and the Hard Drive. Server 1 had (what I
think) is a better drive, therefore the performance should be better
then what I'm seeing compared to Server 2. Most notably is the
difference between the dd test on server 1 and 2 as seen below.
Any suggestions on what to check and what would cause this?
Server 1:
Drive is a Barracuda 7200.12 SATA 6Gb/s 1TB Hard Drive w/64 MB Cache
Running XenServer, test performed @ the non-guest level.
/dev/sda:
Timing cached reads: 43912 MB in 1.99 seconds = 22043.28 MB/sec
Timing buffered disk reads: 344 MB in 3.00 seconds = 114.64 MB/sec
[root@nycxen01 ~]# hdparm /dev/sda
dd if=/dev/zero of=/tmp/output.img bs=8k count=256k
262144+0 records in
262144+0 records out
2147483648 bytes (2.1 GB) copied, 28.0981 seconds, 76.4 MB/s
Server 2:
Drive is a Hitachi Deskstar 7200 SATA 3Gb/s 1TB Drive w/32 MB Cache
Running Debian 6
First, you should use the --direct option for hdparm when doing read tests. This way hdparm tries harder to actually read the data from the drive, and not use the page cache. Also, you could clear the page cache first.
Here are the performance results for my two Samsung Spinpoint F1 1TB (HD103UJ) drives:
Timing O_DIRECT disk reads: 330 MB in 3.02 seconds = 109.37 MB/sec
and on /dev/md2 (a soft-RAID0 of two matching partitions above),
Code:
sudo hdparm --direct /dev/md2
Quote:
/dev/md2:
Timing O_DIRECT disk reads: 640 MB in 3.00 seconds = 213.05 MB/sec
For real-world testing, create a large test file. For example,
Code:
dd if=/dev/urandom of=part bs=1M count=16
cat part part part part > part2 && mv -f part2 part
cat part part part part > part2 && mv -f part2 part
cat part part part part > part2 && mv -f part2 part
cat part part part part > part2 && mv -f part2 part
mv -f part file
This yields a four-gigabyte random file named file .
Using a software RAID0 (striping) on the above two disks (and LVM), a real-world read yields
1048576+0 records in
1048576+0 records out
4294967296 bytes (4,3 GB) copied, 38,7513 s, 111 MB/s
1048576+0 records in
1048576+0 records out
4294967296 bytes (4,3 GB) copied, 41,9995 s, 102 MB/s
[1]- Done dd if=file of=/dev/null bs=4k
[2]+ Done dd if=copy of=/dev/null bs=4k
i.e. a combined read speed of over 210 MB/s.
Pure write speed is difficult to measure. I use a program that pregenerates a megabyte of random data, then permutates it while writing. Let me know if you wish me to post it, so you can test that too. A copy test, which includes both reading and writing on the same partition, is still useful. Just remember that each byte of data is actually both read and written.
1048576+0 records in
1048576+0 records out
4294967296 bytes (4,3 GB) copied, 83,1333 s, 51,7 MB/s
and on RAID0 (striped):
Quote:
1048576+0 records in
1048576+0 records out
4294967296 bytes (4,3 GB) copied, 44,9247 s, 95,6 MB/s
As you can see, using software RAID is definitely worth it. Experiences discussed on the linux kernel mailing list indicate that this scales just like this at least up to six drives; twelve (over 1 gigabyte per second real world read speed) if you use a separate PCI-E card for the SATA controllers (so that the bus bandwidth to the SATA controllers is not a bottleneck).
I've also used 4k block size in the tests, so the results should be close to real-world experience. (I use ext4 and 4096 byte blocks.)
I'm seriously bummed out that I did not get four Samsung F3 1TB drives (for about 60 EUR each, 240 EUR total) before the prices doubled. I manipulate large amounts of data, and having that kind of throughput and storage capacity is very, VERY useful. For a server, you should consider pairing the hard drives (preferably with identical ones, otherwise the slower one will dominate), even considering the current prices. It is definitely easily noticeable in the performance.
While these test just one feature of the drives, and cannot therefore be relied on in comparing the disks, I think you'll find that the Hitachi one is the faster one, if you run the commands above on your servers. And, like I said, disk speed (or lack thereof) is easily noticeable in the performance.
A final note: For some reason, many people did not consider Samsung disks high-end, and Samsung ended up selling the division to Seagate. I've used a lot of disks, and these are the ones I like best. They've been in use for 11334 hours (several years, but not 24/7), with almost 700 power cycles. No reallocated sectors, absolutely no hardware problems. Reliable but cheap, and as you can see in the above results, quite fast too.
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