On Sun, 17 Feb 2008 11:50:25 +0000 pg_lxra@xxxxxxxxxxxxxxxxxx (Peter Grandi) wrote: > >>> On Sat, 16 Feb 2008 20:58:07 -0700, Beolach > >>> <beolach@xxxxxxxxx> said: > > beolach> [ ... ] start w/ 3 drives in RAID5, and add drives as I > beolach> run low on free space, eventually to a total of 14 > beolach> drives (the max the case can fit). > > Like for for so many other posts to this list, all that is > "syntactically" valid is not necessarily the same thing as that > which is wise. > Which part isn't wise? Starting w/ a few drives w/ the intention of growing; or ending w/ a large array (IOW, are 14 drives more than I should put in 1 array & expect to be "safe" from data loss)? > beolach> But when I add the 5th or 6th drive, I'd like to switch > beolach> from RAID5 to RAID6 for the extra redundancy. > > Again, what may be possible is not necessarily what may be wise. > > In particular it seems difficult to discern which usage such > arrays would be put to. There might be a bit of difference > between a giant FAT32 volume containing song lyrics files or an > XFS filesystem with a collection of 500GB tomography scans in > them cached from a large tape backup system. > Sorry for not mentioning, I am planning on using XFS. Its intended usage is general home use; probably most of the space will end up being used by media files that would typically be accessed over the network by MythTV boxes. I'll also be using it as a sandbox database/web/mail server. Everything will just be personal stuff, so if the I did lose it all I would be very depressed, but I hopefully will have all the most important stuff backed up, and I won't lose my job or anything too horrible. The main reason I'm concerned about performance is that for some time after I buy it, it will be the highest speced of my boxes, and so I will also be using it for some gaming, which is where I expect performance to be most noticeable. > beolach> I'm also interested in hearing people's opinions about > beolach> LVM / EVMS. > > They are yellow, and taste of vanilla :-). To say something more > specific is difficult without knowing what kind of requirement > they may be expected to satisfy. > > beolach> I'm currently planning on just using RAID w/out the > beolach> higher level volume management, as from my reading I > beolach> don't think they're worth the performance penalty, [ > beolach> ... ] > > Very amusing that someone who is planning to grow a 3 drive > RAID5 into a 14 drive RAID6 worries about the DM "performance > penalty". > Well, I was reading that LVM2 had a 20%-50% performance penalty, which in my mind is a really big penalty. But I think those numbers where from some time ago, has the situation improved? And is a 14 drive RAID6 going to already have enough overhead that the additional overhead isn't very significant? I'm not sure why you say it's amusing. The other reason I wasn't planning on using LVM was because I was planning on keeping all the drives in the one RAID. If I decide a 14 drive array is too risky, and I go w/ 2 or 3 arrays then LVM would appear much more useful to me. Thanks for the response, Conway S. Smith - 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
