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 store. -- Joseph Landman, Ph.D Founder and CEO Scalable Informatics, Inc. email: landman at scalableinformatics.com web : http://scalableinformatics.com http://scalableinformatics.com/sicluster phone: +1 734 786 8423 x121 fax : +1 866 888 3112 cell : +1 734 612 4615
