Re: [linux-lvm] Power loss consistency for RAID
On Sun, 17 Mar 2019, Zheng Lv wrote: I'm recently considering using software RAID instead of hardware controllers for my home server. AFAIK, write operation on a RAID array is not atomic across disks. I'm concerned that what happens to RAID1/5/6/10 LVs after power loss. Is manual recovery required, or is it automatically checked and repaired on LV activation? Also I'm curious about how such recovery works internally. I use md raid1 and raid10. I recommend that instead of the LVM RAID, which is newer. Create your RAID volumes with md, and add them as PVs: PV VG Fmt Attr PSize PFree /dev/md1 vg_span lvm2 a--u 214.81g 0 /dev/md2 vg_span lvm2 a--u 214.81g 26.72g /dev/md3 vg_span lvm2 a--u 249.00g 148.00g /dev/md4 vg_span lvm2 a--u 252.47g 242.47g Note that you do not need matching drives as with hardware RAID, you can add disks and mix and match partitions of the same size on drives of differing sizes. LVM does this automatically, you have to manually assign partitions to block devices with md. There are very few (large) partitions to assign, so it is a pleasant human sized exercise. While striping and mirror schemes like raid0, raid1, raid10 are actually faster with software RAID, I avoid RAID schemes with RMW cycles like raid5 - you really need the hardware for those. I use raid1 when the filesystem needs to be readable without the md driver - as with /boot. Raid10 provides striping as well as mirroring, with however many drives you have (I usually have 3 or 4). Here is a brief overview of MD recovery and diagnostics. Someone else will have to fill in with the mechanics of LVM raid. Md keeps a version in the superblock of each device in a logical md drive - and marks the older leg as failed and replaced (and begins to sync it). In newer superblock formats, it also keeps a bit map so that it can sync only possibly modified areas. Once a week (configurable), check_raid compares the legs (on most distros). If it encounters a read error on either drive, it immediately syncs that block from the good drive. This reassigns the sector on modern drives. (On ancient drives, a write error on resync marks the drive as failed.) If for some reason (there are legitimate ones involving write optimizations for SWAP volumes and such) the two legs do not match, it arbitrarily copies one leg to the other, keeping a count. (IMO it should also log the block offset so that I can occasionally check that the out of sync occurred in an expected volume.) -- Stuart D. Gathman "Confutatis maledictis, flamis acribus addictis" - background song for a Microsoft sponsored "Where do you want to go from here?" commercial. ___ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
Re: [linux-lvm] Power loss consistency for RAID
but if a RAID got lost, you can always ask to https://www.RecuperoDatiRAIDFasTec.it which is the unique data recovery company that has flat rates for raid recovery starting from 150,00 euro per disk or the other way round, 900 euro for immediate/emergency recovery Messaggio originale Da: lv.zheng.2...@gmail.com Inviato: 18 marzo 2019 10:05 A: linux-lvm@redhat.com Rispondi a: linux-lvm@redhat.com Oggetto: [linux-lvm] Power loss consistency for RAID Dear all, I'm recently considering using software RAID instead of hardware controllers for my home server. AFAIK, write operation on a RAID array is not atomic across disks. I'm concerned that what happens to RAID1/5/6/10 LVs after power loss. Is manual recovery required, or is it automatically checked and repaired on LV activation? Also I'm curious about how such recovery works internally. Many thanks, Zheng Lv ___ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ ___ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
Re: [linux-lvm] Power loss consistency for RAID
it is automatic though you should avoid power losses as better as you can with online PSU against line interactive ones ( which are good for consumer PCs and displays) Messaggio originale Da: lv.zheng.2...@gmail.com Inviato: 18 marzo 2019 10:05 A: linux-lvm@redhat.com Rispondi a: linux-lvm@redhat.com Oggetto: [linux-lvm] Power loss consistency for RAID Dear all, I'm recently considering using software RAID instead of hardware controllers for my home server. AFAIK, write operation on a RAID array is not atomic across disks. I'm concerned that what happens to RAID1/5/6/10 LVs after power loss. Is manual recovery required, or is it automatically checked and repaired on LV activation? Also I'm curious about how such recovery works internally. Many thanks, Zheng Lv ___ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ ___ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
[linux-lvm] Power loss consistency for RAID
Dear all, I'm recently considering using software RAID instead of hardware controllers for my home server. AFAIK, write operation on a RAID array is not atomic across disks. I'm concerned that what happens to RAID1/5/6/10 LVs after power loss. Is manual recovery required, or is it automatically checked and repaired on LV activation? Also I'm curious about how such recovery works internally. Many thanks, Zheng Lv ___ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
