landman at scalableinformatics.com
Fri Apr 22 02:23:32 UTC 2011
On 04/21/2011 08:49 PM, Mohit Anchlia wrote:
> After lot of digging today finaly figured out that it's not really
> using PERC controller but some Fusion MPT. Then it wasn't clear which
PERC is a rebadged LSI based on the 1068E chip.
> tool it supports. Finally I installed lsiutil and was able to change
> the cache size.
> [root at dsdb1 ~]# lspci|grep LSI
> 02:00.0 SCSI storage controller: LSI Logic / Symbios Logic SAS1068E
> PCI-Express Fusion-MPT SAS (rev 08)
This looks like PERC. These are roughly equivalent to the LSI 3081
series. These are not fast units. There is a variant of this that does
RAID6, its usually available as a software update or plugin module
(button?) to this. I might be thinking of the 1078 chip though.
Regardless, these are fairly old designs.
> [root at dsdb1 ~]# dd if=/dev/zero of=/data/big.file bs=128k count=40k oflag=direct
> 1024+0 records in
> 1024+0 records out
> 134217728 bytes (134 MB) copied, 0.742517 seconds, 181 MB/s
> I compared this with SW RAID mdadm that I created yesterday on one of
> the servers and I get around 300MB/s. I will test out first with what
> we have before destroying and testing with mdadm.
So the software RAID is giving you 300 MB/s and the hardware 'RAID' is
giving you ~181 MB/s? Seems a pretty simple choice :)
BTW: The 300MB/s could also be a limitation of the PCIe channel
interconnect (or worse, if they hung the chip off a PCIx bridge). The
motherboard vendors are generally loathe to put more than a few PCIe
lanes for handling SATA, Networking, etc. So typically you wind up with
very low powered 'RAID' and 'SATA/SAS' on the motherboard, connected by
PCIe x2 or x4 at most. A number of motherboards have NICs that are
served by a single PCIe x1 link.
> Thanks for your help that led me to this path. Another question I had
> was when creating mdadm RAID does it make sense to use multipathing?
Well, for a shared backend over a fabric, I'd say possibly. For an
internal connected set, I'd say no. Given what you are doing with
Gluster, I'd say that the additional expense/pain of setting up a
multipath scenario probably isn't worth it.
Gluster lets you get many of these benefits at a higher level in the
stack. Which to a degree, and in some use cases, obviates the need for
multipathing at a lower level. I'd still suggest real RAID at the lower
level (RAID6, and sometimes RAID10 make the most sense) for the backing
Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics, Inc.
email: landman at scalableinformatics.com
web : http://scalableinformatics.com
phone: +1 734 786 8423 x121
fax : +1 866 888 3112
cell : +1 734 612 4615
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