Unix and Linux Stack Exchange
Unix and Linux Stack Exchange

Questions tagged [md]

30 questions
69
votes
2 answers

RAIDing with LVM vs MDRAID - pros and cons?

In his answer to the question "mixed raid types", HBruijn suggests using LVM to implement RAID vs the more standard MDRAID. After a little investigation, it seems LVM also supports RAID functionality. In the past, I have used LVM on top of MDRAID,…
Faheem Mitha
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19
votes
3 answers

Linux md RAID: /dev/md0 vs. /dev/md/0

On newer systems /usr/share/mdadm/mkconf (the script that is used to generate /etc/mdadm/mdadm.conf) tends to use the device name /dev/md/0 instead of /dev/md0: new-system ~ # /usr/share/mdadm/mkconf | grep ARRAY ARRAY /dev/md/0 metadata=1.2…
Martin von Wittich
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9
votes
2 answers

MD device name changing to include "HOSTNAME:" after first reboot. How do I get a consistent name?

On Ubuntu 18.04 I create a RAID 1 array like this: mdadm --create /dev/md/myarray --level=1 --run --raid-devices=2 /dev/sdc /dev/sdd I then add the output of mdadm --detail --scan /dev/md/myarray to /etc/mdadm/mdadm.conf. It looks like this: ARRAY…
EM0
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8
votes
1 answer

md raid5: translate md internal sector numbers to offsets

TL;DR summary: Translate an md sector number into offsets(s) within the /dev/mdX device, and how to investigate it with xfs_db. The sector number is from sh->sector in linux/drivers/md/raid5.c:handle_parity_checks5(). I don't know MD internals, so…
Peter Cordes
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6
votes
1 answer

md raid1 ext3 and 4k sectors slow with directory operations

I recently moved from a hardware RAID1 enclosure to using two eSATA drives with md. Everything seems to be working fine, except for the fact that directory traversals/listings sometimes crawl (on the order of 10s of seconds). I am using an ext3…
zje
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5
votes
2 answers

How does Linux md-RAID handle disk read errors?

There are 2 cases: the read command times out at kernel level (30 seconds by default), the drive reports its unability to read a given sector before the kernel lose patience (the case I'm interested in). Kernel timeout As drive access is…
Totor
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5
votes
1 answer

What are data integrity / bit-rot protection options on CentOS 7?

I have a 2 disk CentOS 7 machine build that I need data integrity / bitrot protection on. How can I achieve this? Note from my reading btrfs,zfs and DM-Integrity does not seem to be options. Btrfs is not an option as btrfs will be deprecated by…
MeData
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5
votes
3 answers

Command 'pvs' says PV device not found, but LVs are mapped and mounted

I had problem with my system (faulty internal power cable). When I got the system back up and running, arrays rebuilding, etc, I seem to have a situation where the pvs command (and vgs and lvs) reports No device found for PV but the logical…
StarNamer
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3
votes
1 answer

linux "mdadm --write-journal" and lvmcache - how do they relate?

In linux mdadm man page I saw the option "--write-journal". How does this relate to lvmcache as lvmcache is built on top of dm-cache? Are they different things or does lvmcache do something like "--write-journal" under the hood? Thanks!
user220574
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3
votes
2 answers

Very poor read performance compared to write performance on md(raid1) / crypt(luks) / lvm

I'm experiencing very poor read performance over raid1/crypt/lvm. In the same time, write speeds are about 2x+ faster on the same setup. On another raid1 setup on the same machine I get normal read speeds (maybe because I'm not using cryptsetup). OS…
Android5360
2
votes
1 answer

What should I expect to see if md/linux RAID is properly compensating for a failing drive?

Does the md subsystem output any messages (to syslog/systemd-journal) to indicate that it's running in a degraded state (or anything else that might indicate that it has successfully reacted to a drive failure, as hinted at here)? For example, I see…
jhfrontz
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2
votes
1 answer

How to wipe md raid meta?

I have Ubuntu 16.04 host with 3 Ubuntu 17.10 guests in KVM (Virtual Machine Manager 1.3.2). I export several block devices from 2 guests to the other guest (let's call it frontend) via iSCSI portal created by targetcli util. Having imported them, I…
ikudyk
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2
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1 answer

EFI system partition on top of MD RAID and LVM

I'd like to put a EFI system partition on top of a MD RAID 1 + LVM setup. So the ESP would be a Logical Volume on top of the MD RAID device. I've heard mixed things about whether this is possible. Has anyone done it? And if so, what issues were…
Faheem Mitha
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2
votes
0 answers

MD RAID 5 module doesn't load at boot

I recently upgraded my NAS to kernel 4.4 and now my md raid 5 array doesn't assemble itself at boot. dmesg reveals this: [ 2.299666] md: personality for level 5 is not loaded! and doing lsmod | grep raid reveals that neither md_mod nor raid456 is…
Scoopta
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2
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0 answers

MD soft-raid to replace fake raid: How to get rid of old metadata?

I had a system running with fake RAID (Intel controller, imsm), which had some problems. Now I'm switching to the regular MD soft-RAID - I created a RAID 1 on /dev/sda1 and /dev/sdb1. Seems to work fine. Unfortunately a run of mdadm --examine…
trapperjohn
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