Questions tagged [device-mapper]
The device mapper is a block layer component which allows the creation of virtual block devices. LVM2 is based on it.
108 questions
1 vote
0 answers
55 views
How to use dm-mirror, or 'dm-raid raid1', with dmsetup only (no LVM automation)?
The goal is to create a mirror (aka raid1) device from two devices (to be mirrored), and (if needed) a third device that serves as the dirty region log / metadata / whatever. That, without using LVM ...
- 149
4 votes
1 answer
373 views
How to get the stats of an lvm cache?
I am using an lvm cache in the most usual combination (small, fast ssd before a huge, slow hdd). It is simply awesome. However, I have not found a way to know, how many blocks are actually cached and ...
- 10.5k
0 votes
0 answers
78 views
Use device mapper snapshots to create multiple versions of the same machine and choose at boot
I already use LVM to create snapshots of volumes, and I recently discovered that device mapper can manage snapshots "manually" without LVM. It would be useful to be able to create a snapshot ...
- 111
2 votes
1 answer
153 views
Is it safe to use a loop device to circumvent EBUSY on a block device underlying device-mapper?
I’m trying to include the beginning of a disk block device (the GPT area) read-only in a device-mapper linear mapping. This block device also contains my root filesystem, as such the partition housing ...
- 21
1 vote
0 answers
104 views
IO wait/failure timeout on iscsi device with multipath enablement
I'm accessing a remote iscsi based SAN using multipath. The network on the server side has known intermittent issues such that there are session failures and path failures/IO failures. I'm not trying ...
- 111
0 votes
1 answer
99 views
udev triggered service not able to run sh script
I am working on a service to capture device-mapper dm-verity uevent. However, I am not able to figure out why the service is able to be triggered but fails to run my logger script. I have the ...
0 votes
0 answers
350 views
Systemd shutdown hanging for 90 seconds due to luks/btrfs
ver since I set up my LUKS-encrypted BTRFS RAID1 between my two NVMe drives on Debian 12, the shutdown process has taken way too long, about a minute and a half. I had to get a video of the shutdown ...
- 1
1 vote
1 answer
74 views
Does dm-crypt waste device space?
That is, when a device-mapping is created manually with the dm-crypt target, is the resulting device smaller than the backing device? What is the missing space used for? Will the answer change ...
- 149
0 votes
1 answer
136 views
Passing an unlocked LUKS partition context from GRUB to Linux?
Question In GRUB one can use the cryptomount command to mount a LUKS partition. Is there a way to pass this decrypted partition to linux such that it appears as a device mapper (/dev/mapper/xxx) entry ...
- 713
0 votes
1 answer
51 views
Device Mapper Snapshot Stored In An Expanding File
Is there a way to create a block device that is backed by a file that grows in size as the block device is written to? I'm looking to use device mapper snapshots (ie: dmsetup create command that ...
- 2,707
4 votes
2 answers
595 views
How can I format a partition in a mapper device?
I created a mapper device with dmsetup and created a partition table with parted: $ fdisk -l /dev/mapper/vdisk Disk /dev/mapper/vdisk: 511.57 GiB, 549295737344 bytes, 1072843237 sectors Units: sectors ...
- 43
0 votes
1 answer
162 views
How to reinstate an invalidated DM snapshot?
I'm using device mapper snapshots. Let's assume that /dev/sda is the read-only origin device, and /dev/sdb is the COW device. I created a persistent snapshot this way: # cat /dev/zero > /dev/sdb # ...
- 149
2 votes
0 answers
80 views
Can't mount extended logical partitions in RAID 0 Fake Array created by dmaid and device mapper
First of all, I would like to let you know I come here cause I'm looking for a solution or a way to be able to mount the HOME partition and to read the inside data. I've been running Funtoo GNU/Linux ...
- 121
3 votes
0 answers
184 views
What's the expected overhead of a passthrough device mapper?
I'm trying to establish a baseline throughput overhead for a passthrough device mapper; i.e. a device mapper that does nothing. Roughly following benchmarking procedures from Cloudflare, I'm measuring ...
- 81
8 votes
2 answers
2k views
How does EXT4 handle sudden lack of space in the underlying storage?
Usually, block device drivers report correct size of the device, and it is possible to actually use all the "available" blocks. So, the filesystem knows how much it can write to such device ...
- 149