Hello,
At this point I probably should state that I am not an experienced
sysadmin. Knowing this, I do have a server management company but they
said they don't know what to do so now I am trying to fix things myself
but I am something of a noob. I normally try to keep my actions to
cautious config changes and testing. I have never done a kernel update.
Any easy way to do this?
Regarding your second advice (to purchase a decent HBA) I have already
thought about it but I guess it comes with it's own drivers that need to
be compiled into initramfs etc. So I am trying to replace the baseboard
with one with SATA3 support to avoid any configuration changes (the old
board has the C202 chipset and the new one has C204 so I guess this
replacement is as simple as it gets - just remove the old board and plug
the new one without any software changes or recompiles). Again I need to
say this server is in production and I can't move the data or the users.
I can have a few hours downtime during the night but that's about all.
Regarding the kernel upgrade, do we need to compile one from source or
there's an easier way?
Thanks!
On 21/04/2013 3:09 AM, Stan Hoeppner wrote:
On 4/19/2013 5:58 PM, Andrei Banu wrote:
I come to you with a difficult problem. We have a server otherwise
snappy fitted with mdraid-1 made of Samsung 840 PRO SSDs. If we copy a
larger file to the server (from the same server, from net doesn't
matter) the server load will increase from roughly 0.7 to over 100 (for
several GB files). Apparently the reason is that the raid can't write well.
...
547682517 bytes (548 MB) copied, 7.99664 s, 68.5 MB/s
547682517 bytes (548 MB) copied, 52.1958 s, 10.5 MB/s
547682517 bytes (548 MB) copied, 75.3476 s, 7.3 MB/s
1073741824 bytes (1.1 GB) copied, 61.8796 s, 17.4 MB/s
Timing buffered disk reads: 654 MB in 3.01 seconds = 217.55 MB/sec
Timing buffered disk reads: 272 MB in 3.01 seconds = 90.44 MB/sec
Timing O_DIRECT disk reads: 788 MB in 3.00 seconds = 262.23 MB/sec
Timing O_DIRECT disk reads: 554 MB in 3.00 seconds = 184.53 MB/sec
...
Obviously this is frustrating, but the fix should be pretty easy.
O/S: CentOS 6.4 / 64 bit (2.6.32-358.2.1.el6.x86_64)
I'd guess your problem is the following regression. I don't believe
this regression is fixed in Red Hat 2.6.32-* kernels:
http://www.archivum.info/linux-ide@xxxxxxxxxxxxxxx/2010-02/00243/bad-performance-with-SSD-since-kernel-version-2.6.32.html
After I discovered this regression and recommended Adam Goryachev
upgrade from Debian 2.6.32 to 3.2.x, his SSD RAID5 throughput increased
by a factor of 5x, though much of this was due testing methods. His raw
SSD throughput more than doubled per drive. The thread detailing this
is long but is a good read:
http://marc.info/?l=linux-raid&m=136098921212920&w=2
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