On Tuesday, September 8, 2015 at 3:50:04 AM UTC-5, Rick Thomas wrote: > Hi Ray, > > I'll try to answer your questions... > > On Sep 7, 2015, at 4:36 PM, ray wrote: > > > Rick, > > > > Thank you for responding and providing all the info. > > > > On Monday, September 7, 2015 at 6:20:07 AM UTC-5, Rick Thomas wrote: > >> On Sep 5, 2015, at 7:24 PM, ray wrote: > >> <snip> > > I have 3 pairs of SSDs, each pair in a RAID0. > > I would use RAID1 on each pair (3 SSDs worth of "usable" space), or RAID5 or > 6 on a larger aggregate. E.g. RAID6 on all 6 drives (gives 4 SSDs worth of > "usable" space), or RAID5 on 6 drives (gives 5 SSDs worth of "usable" space). > Each of those configurations can survive a loss of one SSD (or two, in the > case of RAID6) without data loss. > > Your choice of RAID0 in pairs gives the full 6 SSDs worth of "usable" space, > but has zero redundancy. If that works for you, that's great. > > I've got enough experience (40 years) as a sysadmin to have seen users > tearing hair over lost data (I always had backups -- often tape in those days > -- so the only thing really lost was uptime, but you get the point...) ( When I bought a tape real for the IBM 360, I held onto my boxes of cards for 4 months. I only had to use them once when I overwrote my tape with an empty library. I keep the tape for 5 years until I was sure there would be nothing to that could read it. My new storage was 8" floppies.) > > In case it's not clear, "usable" means space left over after subtracting out > all the redundant data in the array. > > > > >> > >> I configure a small (<1GB) "/boot" partition as a primary partition (e.g. > >> /dev/sda1) on one of the disks, with the same space on the other disk > >> unused. [1] I make another primary partition (e.g. /dev/sd[ab]2), on each > >> of the disks, sized to be one half of the size I want for my swap. The > >> rest of the space on each disk goes into a single, large, logical > >> partition (e.g. /dev/sd[ab]5). Yes, I have made space on other disks for this also. I don't know how to use them but it seemed the redundancy may come in handy. > >> > > This is similar to my setup. I have the swaps on a separate RAID0. > > Should work fine. Of course you should read Pascal's post for a different > point of view.
Yes, those consideration are ringing in my head. It will be a trade-off consideration from now on. > > > > >> The two swap partitions I set up as a RAID0 (e.g. /dev/md0). This will be > >> my system swap. [2] > >> > >> The two large logical partitions, I configure into a RAID1 (e.g. > >> /dev/md1). [3] > >> > > I made my large partition a primary. Could this be problematic? > > It would only be a problem if you need another primary partition for > something. You only get 3 primary partitions on a disk, so I like to leave > one free "just incase". > > > <snip> > >> > > I would like to know more about the purpose of these criteria - please. > > Putting /tmp on tmpfs is for speed. If your /tmp usage fits in RAM (after > allowing for apps, data, and disk buffering) you get RAM speed access to your > temporary data. If it overflows, then the excess goes into swap, so you're > no worse off than if you had /tmp on hard disk in the first place. This can > make large compilations (as an example) run *much* faster. On the other > hand, if you are tight on RAM, putting /tmp on disk doesn't hurt, and > eliminates a source of contention for RAM which is assumed to be a scarce > resource. This sounds like an experiment I will need to exercize. > > The 50% figure is just a rule of thumb I picked up over the years. There's > nothing magic about it. And, as always, YMMV. It's highly application > dependent. > > > <snip> > > It might make sense to create a logical volume with some of the unused space > in the volume group called (for lack of a better name) /backup. It's > "reliable" in the sense that it resides on a RAID1/5/6 array, so it's a good > place to put your backups of things like /boot. For "ultimate" backup, I > usually use huge (e.g. 4TB or larger) external USB disk drives. I don't RAID > them, instead I have two or three and rotate amongst them using each one for > a week, then swapping it out for the next one. The currently offline > drive(s) I keep in a fire-proof safe, preferably in a separate building from > the server... > Thanks, Ray
