I never depend on RAID either RAID5 or mirroring for backup purposes. RAID's usefulness is if in the middle of the day (or in the middle of a backup) a hard drive fails then the server does not unceremoniously shut down.
Instead I can take a final backup of the server then do whatever to replace the disk With hardware RAID cards that may simply mean swapping the failed disk and the hardware card takes care of rebuilding the array by itself. With software that may mean the array is scotched. I have attempted in the past to replace disks on software arrays. Sometimes it works sometimes it does not. Sometimes in the process of rebuilding the primary disk craps out. With small "desktop" servers I use mirroring simply because disks nowadays are cheap, and I'll use whatever RAID is available. Often it's so-called "fakeraid" because that way the server will boot off the "raid" array. Since the disks in these are purchased at the same time, when 1 goes I usually just replace both if they are out of warranty (and they usually are) recreate the array and restore from backup. Often I'll regen the entire server. I have several servers with "fakeraid" chips in them and they are 1U with only 2 slots for disks, so they have mirrored disks in them, and the process to get the OS installed and working so that the system will boot off the "raid" array is so cumbersome that it isn't even possible to upgrade the OS. Ubuntu's developers in particular hate fakeraid with a passion and in every new version are constantly screwing with the drivers so you have to find new ways to set them up. Some fakeraid chips write metadata to the end of the disk and GPT tables will overwrite those so I have to setup the disks as MBR (and no larger than 2TB of course) It's usually a lot of fun to update to a new version on these. But, the 1U server form factor is pretty restrictive in terms of what disks you can use. For cost most of the time I use 3.5" SATA disks. I have not found SAS drives to be worth the money, I'll spec em for customers since they will lay out the cash for them but I use disks I can buy over the counter for my personal stuff. It is a constant battle with disk drive makers who seem to have forgotten that the I in raid means INEXPENSIVE drives, not "independent" drives. They have prices jacked up sky high for anything that they think isn't going to retail. Ted -----Original Message----- From: PLUG <plug-boun...@pdxlinux.org> On Behalf Of Rich Shepard Sent: Friday, March 24, 2023 9:37 AM To: Portland Linux/Unix Group <plug@pdxlinux.org> Subject: Re: [PLUG] External drive issue On Fri, 24 Mar 2023, Rich Shepard wrote: > Checking cfdisk for both /dev/sde and /dev/sdf shows both having free > space for the entire disk. A question for the professional sysadmins: having both disks in a mirrored RAID1 array as a logical volumn fail, does it make sense to rebuild the RAID, vgs and lv? Since a mirrored copy didn't save my backup history, perhaps I should use only one disk for backp and save the other as a spare. Your professional opinion? TIA, Rich
