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Description of problem:
When creating VDO with --readCacheSize value set to something extremely (stupidly) high --readCacheSize="8000E", vdo is created without issues. The issue might come sometime in the future where the user might even loose some data when his server runs out of memory.
As adding more restriction to user is not a good thing, can you please make few different changes here?
1) Add a warning to docs,. something along these lines:
"Warning: setting this value to high can cause the system to run out of memory and hang"
2) Check for actual memory size and in case this value is larger, make the user acknowledge this might be a risk.
Version-Release number of selected component (if applicable):
vdo-6.1.0.0-6.x86_64
How reproducible:
100%
Steps to Reproduce:
1. # vdo create --device=/dev/sdc --name=vdo_test --readCacheSize=8000E --readCache=enabled
2. # vdo status --all | grep "Read cache size"
Read cache size: 8000E
Actual results:
VDO created with readCacheSize
Expected results:
Explicit warning / prompt for user to acknowledge this value
Additional info:
Looking at this issue it seems that setting the readCacheSize to a more
reasonable value of 1T (knowing that my system doesn't have 1T of memory), VDO
returns with an error messages.
parkst-26:/permabit/user/dkeefe# vdo start --name=my_vdo --verbose
Starting VDO my_vdo
dmsetup status my_vdo
modprobe kvdo
dmsetup create my_vdo --table '0 8589934592 dedupe /dev/sda1 4096 enabled 268435456 32768 16380 on async my_vdo ack=1,bio=4,bioRotationInterval=64,cpu=6,hash=1,logical=5,physical=2'
vdo: ERROR - Could not set up device mapper for my_vdo
vdo: ERROR - device-mapper: reload ioctl on my_vdo failed: Cannot allocate memory.
VDO will correctly error out when it can not allocate memory up to a read
cache size of 31T. For configurations of 32T or larger VDO will not report
any problems. Smells like a bug.
Tested with vdo-6.1.0.46-9:
# vdo create --device=/dev/sda3 --name=vdo --readCacheSize=8000E --readCache=enabled
Usage: vdo --name=<volume>|--all [<option>...] activate|deactivate|create|remove|
start|stop|status|list|modify|
changeWritePolicy|enableDeduplication|
disableDeduplication|enableCompression|
disableCompression|growLogical|growPhysical|
printConfigFile
vdo: error: option --readCacheSize: must be at least 0M and less than 16T
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHEA-2018:0871
Description of problem: When creating VDO with --readCacheSize value set to something extremely (stupidly) high --readCacheSize="8000E", vdo is created without issues. The issue might come sometime in the future where the user might even loose some data when his server runs out of memory. As adding more restriction to user is not a good thing, can you please make few different changes here? 1) Add a warning to docs,. something along these lines: "Warning: setting this value to high can cause the system to run out of memory and hang" 2) Check for actual memory size and in case this value is larger, make the user acknowledge this might be a risk. Version-Release number of selected component (if applicable): vdo-6.1.0.0-6.x86_64 How reproducible: 100% Steps to Reproduce: 1. # vdo create --device=/dev/sdc --name=vdo_test --readCacheSize=8000E --readCache=enabled 2. # vdo status --all | grep "Read cache size" Read cache size: 8000E Actual results: VDO created with readCacheSize Expected results: Explicit warning / prompt for user to acknowledge this value Additional info: