First off: Your file system may not have checksums, but your hard drive itself has them. There’s S.M.A.R.T., for example. Once one bit too many got flipped, the error can’t be corrected, of course. And if you’re really unlucky, bits can change in such a way that the checksum won’t become invalid; then the error … Read more
Your current setup is like this: “https://serverfault.com/” /var | /usr | /home | ————————– | LVM Volume | ————————– | RAID Volume | ————————– | Disk 1 | Disk 2 | Disk 3 | It’s a much simpler setup with more flexibility. You can use all of the disks in the RAID volume and slice … Read more
If your array is md0 then echo “idle” > /sys/block/md0/md/sync_action ‘idle’ will stop an active resync/recovery etc. There is no guarantee that another resync/recovery may not be automatically started again, though some event will be needed to trigger this. http://www.mjmwired.net/kernel/Documentation/md.txt#477
Let’s try to reply one question at a time: Is TRIM support necessary for modern (2015-2016 era) SSDs? Short answer: in most cases, no. Long answer: if you reserve sufficient spare space (~20%), even consumer-grade drive usually have quite good performance consistency values (but you need to avoid the drives which, instead, choke on sustained … Read more
I prefer HW raid, ’cause if you have to pull good disks out of a dead machine you’re not limited to the OS configuration of the raid “array”. You do keep backups of your RAID controllers config, don’t you? So just load that up on a donor machine, slot in the drives (in the right … Read more
In short: if using a low-end RAID card (without cache), do yourself a favor and switch to software RAID. If using a mid-to-high-end card (with BBU or NVRAM), then hardware is often (but not always! see below) a good choice. Long answer: when computing power was limited, hardware RAID cards had the significant advantage to … Read more
I use kexec-reboot on nearly all of my production systems. It works incredibly well, allowing me to bypass the long POST time on HP ProLiant servers and reduce the boot cycle from 5 minutes to ~45 seconds. See: https://github.com/error10/kexec-reboot The only caveat is that it doesn’t seem to work on RHEL/CentOS 6.x systems booting UEFI. … Read more
In practice, people who buy from enterprise vendors (HPE, Dell, etc.) do not worry about this. Drives sourced by these vendors are already spread across multiple manufacturers under the same part number. An HP disk under a particular SKU may be HGST or Seagate or Western Digital. Same HP part number, variation on manufacturer, lot … Read more
RAID guards against one kind of hardware failure. There’s lots of failure modes that it doesn’t guard against. File corruption Human error (deleting files by mistake) Catastrophic damage (someone dumps water onto the server) Viruses and other malware Software bugs that wipe out data Hardware problems that wipe out data or cause hardware damage (controller … Read more
RAID: Why and When RAID stands for Redundant Array of Independent Disks (some are taught “Inexpensive” to indicate that they are “normal” disks; historically there were internally redundant disks which were very expensive; since those are no longer available the acronym has adapted). At the most general level, a RAID is a group of disks … Read more