Sorry for taking so long to reply but it's been a hectic week. Thanks for your reply. Out of curiousity, what is MD's linear personality or DM? Would this affect performance if I expanded my RAID using this? --- Molle Bestefich <molle.bestefich@xxxxxxxxx> wrote: > Rik Herrin wrote: > > I was interested in Linux's RAID capabilities and > > read that mdadm was the tool of choice. We are > > currently comparing software RAID with hardware > RAID > > MD is far superior to most of the hardware RAID > solutions I've touched. > In short, it seems MD is developed with the goal of > keeping your data > safe, not selling hardware. > > I've had problems both with MD and with hardware > RAID. With hardware > RAID, once things go bad, they really go bad. With > MD, there's > usually a straight-forward way to rescue things. > And when there's > not, Neil's a real nice guy who always stands up to > help and fix bugs. > > I would trust my data with MD over any hardware RAID > solution, > including professional server RAID solutions from > eg. Compaq or IBM. > > MD is a little more difficult to set up and also > lacks in that it > doesn't integrate with BIOS level stuff and boot > loaders (maybe > there's minimal MD RAID 1 support in Lilo, not > sure). Depending on > your choice of hardware, you might also get more > features than MD can > currently offer. > > > 1) OCE: Online Capacity Expansion: From the > latest > > version of mdadm (v2.2), it ssems that there is > > support for it with the -G option. How well > tested is > > this? > > New feature, so obviously not tested very well. > > Neil said at one point that he was going to release > this to the > general public when it's stable and when it can > recover an interrupted > resize process. Sounds like a very reasonable and > sane goal to me, I > hope that this is still the case. > > Otherwise, it's easy to work around - you can just > create a new RAID > array on your new disks / extra disk space and then > join it to the end > of the old array using MD's linear personality or > DM. Never tried it, > but should work just fine. > > > Also, in the Readme / Man page, it mentions: > > This usage causes mdadm to attempt to > reconfigure a > > running array. This is only possibly if the > kernel > > being used supports a particular reconfiguration. > > How can I know if the kernel I am using supports > this > > reconfiguration? What if I'm compiling the kernel > by > > hand. What options would I have to enable? > > Just the usual MD stuff I think. > You'll probably need a quite new kernel where Neil's > bitmap patches > has been applied. > Hopefully MD will detect whether the kernel is new > enough or not, but > I haven't tried myself ;-). > > > 2) RAID Level Migration: Does mdadm currently > > support this feature? > > I don't think so, but sounds like RAID5 --> RAID6 is > planned. > Check back in a year or so ;-). > > Or choose the RAID level you *really* want to begin > with (duh). > > Since you say "we", I assume you're part of a very > large corporation > and thus intend to RAID a whole bunch of disks. Go > with RAID6 + a > couple of spares for that. If you intend to use > really many disks, > make multiple arrays. (Not sure whether you can > share spares across > arrays, but I think you can.) > > > 3) Performance issues: I'm currently thinking of > > using either RAID 10 or LVM2 with RAID 5 to serve > as a > > RAID server. The machine will be running either > an > > AMD 64 processor or a dual-core AMD 64 processor, > so I > > don't think the CPU will be a bottleneck. In > fact, it > > should easily pass the speed of most "hardware" > based > > RAID systems. > > I think there's two issues to cover, > * Throughput > * Seek times > > And of course they're not entirely separate issues - > throughput will > be lower when you're doing random access (seeking) > and seek times will > be higher when you're pulling lots of data out. > > I've seen lots of MD tests, but none that covered > profiling MD's > random access performance. So I suppose that most > hardware solutions > will do a lot better than MD here since they have > been profiled with > this in mind. > > Throughput-wise, I think MD is probably very good. > But I can't back that up with factual data, sorry. > > > 4) Would anyone recommend a certain hotswap > > enclosure? > > I would, but can't remember their name, sorry :-) > __________________________________ Yahoo! for Good - Make a difference this year. http://brand.yahoo.com/cybergivingweek2005/ - 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
