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we noticed really bad write performance, on our new Dell R720 with Perc 710. Especially when it come to writing a lot of small files. The funny thing is that this bad performance only occurs on newer linux distributions like ubuntu 14.04. or latest centos. Doing the same operation on
Ubuntu 10.04 or other distributions from around 2012 the performance is okay. I fear it's related to something in the kernel like new megaraid_sas driver ?

Below you can see some of the configurations and tests i was using/doing.

Setup:
Dell R720
RAID: PERC 710 Mini Rev: 21.3.011 -00009
HDD: 2x600GB 15K SAS SEAGATE  ST3450857SS

Raid 1
Write Policy: Write Back
Read Policy: Read Ahead
Disc Cache: Enabled
Filesystem: tested with xfs and ext4 
lspci: 03:00.0 RAID bus controller: LSI Logic / Symbios Logic MegaRAID SAS 2208 [Thunderbolt] (rev 05)

Results Ubuntu 14.04:

dd if=/dev/zero of=/root/testfile bs=512 count=10000 oflag=dsync
10000+0 records in
10000+0 records out
5120000 bytes (5.1 MB) copied, 1.33572 s, 3.8 MB/s

Results Ubuntu 10.04:

dd if=/dev/zero of=/root/testfile bs=512 count=10000 oflag=dsync
10000+0 records in
10000+0 records out
5120000 bytes (5.1 MB) copied, 0.702619 s, 7.3 MB/s

The same results i got on a Dell R710 which has the PERC H700.

I wonder if anyone has a solution to that or a recommendation for a RAID Controller card which works better with the mega_raid_sas driver or uses another driver ?

btw: I did an IOMeter Test according to Dell, same poor results on latest Linux distribution e.g. Redhat. On Windows it works fine, so really looks like a driver/kernel Problem.

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