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Just like we have 'writeerror_dev' supporting creation of device
which 'readable' segment and segments where write will fail we
have now support for delay zero mappings.
This is useful if we want to 'fake' large writing areas where we do
not really care about the actual 'disk' content - since we test
operation logic and it doesn't matter we read and write zeroes.
With combination with 'delay' target we can create specific mappings
and avoid using large memory areas of ramdisk.
dm-integrity stores checksums of the data written to an
LV, and returns an error if data read from the LV does
not match the previously saved checksum. When used on
raid images, dm-raid will correct the error by reading
the block from another image, and the device user sees
no error. The integrity metadata (checksums) are stored
on an internal LV allocated by lvm for each linear image.
The internal LV is allocated on the same PV as the image.
Create a raid LV with an integrity layer over each
raid image (for raid levels 1,4,5,6,10):
lvcreate --type raidN --raidintegrity y [options]
Add an integrity layer to images of an existing raid LV:
lvconvert --raidintegrity y LV
Remove the integrity layer from images of a raid LV:
lvconvert --raidintegrity n LV
Settings
Use --raidintegritymode journal|bitmap (journal is default)
to configure the method used by dm-integrity to ensure
crash consistency.
Initialization
When integrity is added to an LV, the kernel needs to
initialize the integrity metadata/checksums for all blocks
in the LV. The data corruption checking performed by
dm-integrity will only operate on areas of the LV that
are already initialized. The progress of integrity
initialization is reported by the "syncpercent" LV
reporting field (and under the Cpy%Sync lvs column.)
Example: create a raid1 LV with integrity:
$ lvcreate --type raid1 -m1 --raidintegrity y -n rr -L1G foo
Creating integrity metadata LV rr_rimage_0_imeta with size 12.00 MiB.
Logical volume "rr_rimage_0_imeta" created.
Creating integrity metadata LV rr_rimage_1_imeta with size 12.00 MiB.
Logical volume "rr_rimage_1_imeta" created.
Logical volume "rr" created.
$ lvs -a foo
LV VG Attr LSize Origin Cpy%Sync
rr foo rwi-a-r--- 1.00g 4.93
[rr_rimage_0] foo gwi-aor--- 1.00g [rr_rimage_0_iorig] 41.02
[rr_rimage_0_imeta] foo ewi-ao---- 12.00m
[rr_rimage_0_iorig] foo -wi-ao---- 1.00g
[rr_rimage_1] foo gwi-aor--- 1.00g [rr_rimage_1_iorig] 39.45
[rr_rimage_1_imeta] foo ewi-ao---- 12.00m
[rr_rimage_1_iorig] foo -wi-ao---- 1.00g
[rr_rmeta_0] foo ewi-aor--- 4.00m
[rr_rmeta_1] foo ewi-aor--- 4.00m
Use /dev/md33 instead of /dev/md0 to reduce chances of
conflicting with an existing name.
Only call 'mdadm --stop /dev/md33' for cleanup and don't
use 'mdadm --stop --scan' to avoid stopping other md devs.
Since we use 'set -euE -o pipefail' for shell execution,
any failure of any command in the 'piped' shell can result
in failure of whole executed chain - resulting in typically
unsually test skip, that was left unnoticed.
Since checked command have usually short output, the simplest
fix seems to be to let grep parse whole output instead
of quiting after first match.
So when the target name happened to be a suffix of another one,
the grep was filtering incorrect line
(i.e. dm-cache && dm-writecache) - so do a line head matching.
Unfortunatelly on kernels <4.16 lvm2 can't user brd ramdisks
for backend device as number of test is failing with this kernel
message:
device-mapper: ioctl: can't change device type after initial table load.
caused by DAX request-based handling, and lvm2 tries to replace device
with backend 'error' bio-based device and such table reload is being
rejected.
So ATM keep ramdisk only on most recent kernel to experiment a bit,
for older machines just stay safe and keep old slower loop backend.
Just like 52656c89fd
when now cache is compiled in 'unditionally'.
This patch is actually enforce by changes in
commit: 2bc896f2a3
where CACHE value is not set anymore.
Usage of dm_delay looks to be slowing not just 'delayed' portion
of device, but due to the fact it's also slows down ANY flush
operation on such device it's overal speed impact is huge.
In some case we can however user other methods to slowdown disk writes,
in case of old dm 'mirror' target we can throttle I/O of mirror
synchronisation giving the next commands enough time to test couple
race conditions.
Usage:
throttle_dm_mirror [percentage]
Thtrottle down sync speed (lowest is '1' which is also default when
unspecified)
restore_dm_mirror
Restores the value of throttling before call of 'throttle_dm_mirror'
Usually it should '100'
Currently usage of loop device over backend file in ramdisk (tmpfs)
is actually causing unnecassary memory consution, since just
reading such loop device is causing RAM provisioning.
This patch add another possible way how to use ramdisk directly
through 'brd' device when possible (and allowed).
This however has it's limitation as well - brd does not support
TRIM, so the only way how to erase is to remove brd module ??
Alse there is 4K sector size limitation imposed by ramdisk.
Anyway - for some mirror test that were using large amount of
disk space (tens of MB) this brings noticable speed boost.
(But could be worth to solve the slowness of loop in kernel?)
To prevent using 'brd' for testing set LVM_TEST_PREFER_BRD=0
like this:
make check_local LVM_TEST_PREFER_BRD=0
When 'dmsetup' reports result with --nameprefixes it currently
incorrectly 'escapes' problematic characters.
Letting pass such string though shell 'eval' function is hard task.
So instead cut away substring.
Once dmsetup will start to properly escape backslash and apostrophe
this function may need further tuning.
