Re: Incredibly poor performance of mdraid-1 with 2 SSD Samsung 840 PRO

[Stan Hoeppner <stan@hardwarefreak.com>]

On 4/19/2013 5:58 PM, Andrei Banu wrote:
> Hardware: SuperMicro 5017C-MTRF

Not relevant if you're using SATA ports 0-1, but may well be if using
2-5, assuming this system isn't brand new.  As I said previously, you'd
see some errors in dmesg if you had port/cable issues.  From:

Intel® 6 Series Chipset and Intel® C200 Series Chipset Specification Update


Problem:  Due to a circuit design issue on Intel 6 Series Chipset and
Intel C200 Series Chipset, electrical lifetime wear out may affect clock
distribution for SATA ports 2-5. This may manifest itself as a
functional issue on SATA ports 2-5 over time.

•The electrical lifetime wear out may result in device oxide degradation
which over time can cause drain to gate leakage current.

•This issue has time, temperature and voltage sensitivities.

Implication:  The increased leakage current may result in an unstable
clock and potentially functional issues on SATA ports 2-5 in the form of
receive errors, transmit errors, and unrecognized drives.

...
•SATA ports 0-1 are not affected by this design issue as they have
separate clock generation circuitry.

Workaround:  Intel has worked with board and system manufacturers to
identify and implement solutions for affected systems.

•Use only SATA ports 0-1.
•Use an add-in PCIe SATA bridge solution.


Not all boards are affected by this.  You'd have to check the spec
revision on your C202, which means contacting SuperMicro with your board
revision/serial number.  To be certain you're not affected simply use
only ports 0-1.  But on that note...

It may be an opportune time to consider dropping in a LSI 9211-4i.
4GB/s raw throughput, plenty for 4 SSDs at full boogie should you
expand.  The kit version comes with a 1-4 breakout cable for your 1U SM
chassis drive backplane.  Even if we get your issue fixed via software
and both drives are humming away at ~260MB/s, that nightly backup
process you mentioned, and others, would surely benefit from an
additional ~200MB/s throughput.

-- 
Stan

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