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Mapping part of a block device: dmsetup vs losetup

Suppose I want to create a virtual block device from an area on already existing block device. I can use either dmsetup (device mapper) or losetup for this purpose. What are practical differences ...
1
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0answers
64 views

How can I xor two block devices together?

I'm looking for a way to create a virtual block device that when accessed returns the XOR of two block devices. I feel like dmsetup would be used here somewhere but I can't find anything related to ...
0
votes
1answer
81 views

Have an SSD and HDD as the same filesystem and overflow from one to the other?

Is it possible in Linux (specifically OpenSUSE) to have an SSD and a HDD set up in such a way that they appear as a single filesystem, yet data is always written to the SSD until full, and then "...
0
votes
1answer
383 views

Can't create persistent snapshot device with `dmsetup`

I am trying to create a dmsetup snapshot device be able to rollback changes made by fsck. I think I'm calling dmsetup incorrectly. Here's an example: $ truncate -s 4096 real snapshot $...
2
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0answers
490 views

Create a block device made of files

TL;DR: Given 2TB worth of 4MB files, how would I create a block device with those files as backing storage? Background I want to trial use of Sia for storage, since: Storing 1TB on Sia costs ...
1
vote
1answer
87 views

Is Block device aware of the actual user/process which initiates read/write?

The VFS knows which user/process has sent read/write request. Is the actual block device aware of these details. Does 'bio' struct contain any details which point to the user space parameters? Using ...
3
votes
1answer
145 views

Can I tell whether a block device is in use?

Let's assume this is based on device-mapper. How can I tell if a given block device is already in use? (For example, a PV of a currently in use VG, or a encrypted LUKS device that is currently ...
2
votes
2answers
3k views

How can I tell if a encrypted (LUKS) device is already open?

Is there a way to tell, given a path to a LUKS block device, and not knowing the passphrase, whether the device is already open (decrypted)? What about knowing the path to the decrypted device?
4
votes
0answers
349 views

How to cache block devices (for device mapper)?

problem / observed effect It seems that the page cache ignores block devices which are not opened. And worse: Reads from device mapper (DM) devices which use a cached device are not cached at all (...
0
votes
3answers
116 views

Can we predict the next registered SCSI mass storage device name

I need to anticipate the device name (sdX) that the next mass storage device (sda, sdb, sdc, …) will receive from the SCSI driver. If I remove one device and connect another one, I noticed that the ...