On Wed, Sep 15, 2010 at 03:41:01PM -0500, Stan Hoeppner wrote: > Pol Hallen put forth on 9/15/2010 3:07 PM: > > Hello all :-) > > > > I think about a low cost raid 6 hardware (6 disks): > > > > On the motherboard 3 pci controllers (sil3114 > > http://www.siliconimage.com/products/product.aspx?pid=28) cost for each > > about 10/15euro > > > > and 2 disks by controllers > > > > So I've 6 disks (raid 6 with mdadm) and if a controller breaks raid 6 > > should be clean. > > > > Is it a acceptable situation or I don't consider other unexpected? > > Is your goal strictly to build a RAID6 setup, or is this a means to an > end. If you're merely excited by the concept of RAID6 then this hardware > setup should be fine. With modern SATA drives, keep in mind that any > one of those six disks can nearly saturate the PCI bus. So with 6 disks > you're only getting about 1/6th of the performance of the drives, or > 133MB/s maximum data rate. > > Most mid range mobos come with 4-6 SATA ports these days. You'd be > better off overall, performance wise and money spent, if you used 4 mobo > SATA ports connected to the same SATA chip (some come with multiple SATA > chips--you want all drives connected to the same chip) and RAID5 instead > of 6. You'd save the cost of 2 drives and 3 PCI SATA cards, which would > be enough to pay for the new mobo/CPU/RAM. You'd have far better > performance for the same money. With four SATA drives on a new mobo > with an AHCI chip you'd see over 400 MB/s, about 4 times that of the PCI > 6 drive solution. You'd have one drive less worth of capacity. > > If I were you, I'd actually go with RAID 10 (1+0) over the 4 drives. > You only end up with 2 disks worth of capacity, but you'll get _much_ > better performance, especially with writes. Additionally, in the event > of a disk failure, rebuilding a 6x1TB RAID5/6 array will take forever > and a day. With RAID 10 drive rebuilds are typically many many times > faster. > > Get yourself a new AHCI mobo with 4 SATA ports on one chip, 4 x 1TB or > 2TB 7.2k WD Blue drives, and configure them as a md RAID10. You'll get > great performance, fast rebuild times, 1 or 2 TB of capacity, and the > ability to sustain up to two drive failures, as long as they are not > members of the same mirror set. I concur with much of what Stan writes. If at all possible, use the SATA ports on the motherboard. Or buy a new motherboard, some come with 8 SATA ports, for not a big extra cost. These ports are connected to the south bridge often with 20 Tbit/s or more, while a controller on an 32 bit PCI only delivers 1 TBit. For the RAID type, raid 5 and 6 do have good performance for sequential read and write, while random access is mediocre. raid10 in the linux sence (not raid1+0) gives good performance, almost raid0i sequential read performance for raid10,f1 best regards keld -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
