I agree with Volker, but for slightly different reasons. Software RAID-1 is the only way to go :-)
Unless you already understand the tradeoffs (which includes understanding that the I in RAID stands for "inexpensive", so using RAID-5 to "get more disk space" is doomed to messy failure, because the MTBF for disks these days is out of balance with their storage capacity; i.e. it takes too long to rebuild RAID5, and almost too long to rebuild RAID6 even), RAID-1 has the most stable and "understandable" failure position. Hardware RAID is only stable if you have replacement opportunities for the controller. Once that goes, the whole array is useless unless you can get an identical replacement (same FW version too, often). I've replaced a lot of disks over the years, and once I stopped messing around and went SW RAID-1 everywhere disk failures & replacements became much less stressful. The last one to go was the boot disk for my new workstation (SSD lifetimes are terribly low) ... no problems, nothing stopped working, disk replaced (warranty), array rebuilt, everything happy again in almost no time ... -jim On Mon, Apr 27, 2015 at 4:26 PM, Volker Kuhlmann <list0...@paradise.net.nz> wrote: > On Mon 27 Apr 2015 15:07:37 NZST +1200, Peter Simmonds wrote: > >> My own logic with software vs hardware raid is that the Linux SW >> raid drivers may only possibly be written in C, whereas the firmware >> on a raid card is likely written in i386 assembly language and >> packed into a flash ROM. C, while it uses optimizations through the >> compiler, I would be guessing produces much fatter code than asm >> i386 would be. > > Forget about your language thoughts here, you're in the wrong forest. > You need to distinguish 3 types of raid implementation (and discard > everything raid manufacturers' marketroidal spins spurt forth on theri > websites): > > 1) Hardware RAID. The data goes over the PCI bus only once, and is > distributed to the actual disks by a beefy computer on the raid card > with plenty of RAM and often battery backup (for that RAM). To the OS > the card appears as a single drive. You buy desktop computers for less > than the cost of one of those cards. If the card dies you buy a new one > to get your data back. > > 2) Software RAID. Data is duplicated by the main CPU and goes over the > PCI bus once for each disk (writing, reading if checksumming is needed > by your chosen RAID level). There is high flexibility in configuring the > disks, you don't have to use whole disks for RAID, you can use just one > partition. It doesn't even have to be the same partition on each disk > either. If the SATA controller dies you plug the disks into another box > and are back up running. Depending on the raid level you can get access > to the data by-passing the raid, in a crunch. > > 3) Fake RAID. This is combining the worst of 1) and 2). It's what you get > for 10 bucks extra on a SATA card, or free with your mobo. Promise > FastCrap(TM) springs to mind prominently (I don't think they've ever > made anything decent, but have infinite ways of weasle-wording their > rubbish into hardware RAID). You need a proprietory driver(!!) to be > able to use it. Your data flows the same way as in 2). If the card dies > you are close to f..inished. These are consumer "products". > > Either spend the money or make do with Linux SW RAID. Don't fake it, or > don't whinge if you do. > > The RAID checksumming consists of integer operations on modern CPUs. It > will be highly optimised (there is assembler on some parts of the Linux > kernel). You can of course just do a quick install and test whether it's > fast enough for you. > > It also depends on what RAID level you're going for. You could also > upgrade from SW to HW RAID later. I use SW RAID 1 in all my desktops > because it means I don't have downtime, and it's possible to mirror > smaller with larger disks (not mirroring all of the larger disk, which > is intentional). > > Volker > > -- > Volker Kuhlmann > http://volker.top.geek.nz/ Please do not CC list postings to me. > _______________________________________________ > Linux-users mailing list > Linux-users@lists.canterbury.ac.nz > http://lists.canterbury.ac.nz/mailman/listinfo/linux-users _______________________________________________ Linux-users mailing list Linux-users@lists.canterbury.ac.nz http://lists.canterbury.ac.nz/mailman/listinfo/linux-users
