mars/kernel/Kconfig

#
# MARS configuration
#

config MARS
	tristate "block storage replication MARS"
	depends on m
	depends on BLOCK && PROC_SYSCTL && HIGH_RES_TIMERS
	default n
	select CRYPTO_MD5
	select CRYPTO_CRC32
	select CRYPTO_CRC32C
	---help---
	See https://github.com/schoebel/mars/docu/
	Only compile as a module!

config MARS_BENCHMARK
	bool "rough measurement of digest and compression algorithms"
	depends on MARS
	default y
	---help---
	Upon modprobe mars, display some rough measurements in
	nanoseconds. Note that results may depend on the compressibility
	of test data. Thus take the results with a grain of salt
	(similarly to BogoMIPS).
	If unsure, say Y here.

config MARS_CHECKS
	bool "enable simple runtime checks in MARS"
	depends on MARS
	default y
	---help---
	These checks should be rather lightweight. Use them
	for beta testing and for production systems where
	safety is more important than performance.
	In case of bugs in the reference counting, an automatic	repair
	is attempted, which lowers the risk of memory corruptions.
	Disable only if you need the absolutely last grain of
	performance.
	If unsure, say Y here.

config MARS_DEBUG
	bool "enable full runtime checks and some tracing in MARS"
	depends on MARS
	default n
	---help---
	Some of these checks and some additional error tracing may
	consume noticable amounts of memory.
	OFF for production systems. ON for testing!

config MARS_DEBUG_DEFAULT
	bool "turn on debug messages by default (may flood the logfiles)"
	depends on MARS_DEBUG
	default n
	---help---
	normally OFF

config MARS_DEBUG_MEM
	bool "debug memory operations"
	depends on MARS_DEBUG
	default n
	---help---
	This adds considerable space and time overhead, but catches
	many errors (including some that are not caught by kmemleak).
	Use only for development and thorough testing!

config MARS_DEBUG_MEM_STRONG
	bool "intensified debugging of memory operations"
	depends on MARS_DEBUG_MEM
	default y
	---help---
	Trace all block allocations, find more errors.
	Adds some overhead.
	Use for debugging of new bricks or for intensified
	regression testing.

config MARS_DEBUG_ORDER0
	bool "also debug order0 operations"
	depends on MARS_DEBUG_MEM
	default n
	---help---
	Turn even order 0 allocations into order 1 ones and provoke
	heavy memory fragmentation problems from the buddy allocator,
	but catch some additional memory problems.
	Use only if you know what you are doing!
	Normally OFF.

config MARS_DEFAULT_PORT
	int "port number where MARS is listening"
	depends on MARS
	default 7777
	---help---
	Best practice is to uniformly use the same port number
	in a cluster. Therefore, this is a compiletime constant.
	You may override this at insmod time via the mars_port= parameter.

config MARS_SEPARATE_PORTS
	bool "use separate port numbers for traffic shaping"
	depends on MARS
	default y
	---help---
	When enabled, the following port assignments will be used:

	  CONFIG_MARS_DEFAULT_PORT     : updates of symlinks
	  CONFIG_MARS_DEFAULT_PORT + 1 : replication of logfiles
	  CONFIG_MARS_DEFAULT_PORT + 2 : (initial) sync traffic

	As a consequence, external traffic shaping may be used to
	individually control the network speed for different types
	of traffic.

	Please don't hinder the symlink updates in any way -- they are
	most vital, and they produce no mass traffic at all
	(it's only some kind of  meta-information traffic).

	Say Y if you have a big datacenter.
	Say N if you cannot afford a bigger hole in your firefall.
	If unsure, say Y.


config MARS_IPv4_TOS
	bool "use TOS / DSCP in IPv4"
	depends on MARS_SEPARATE_PORTS
	default y
	---help---
	Tag IP traffic differently for different ports.
	In certain private networks, this can improve certain
	network bottlenecks.

config MARS_MEM_RETRY
	bool "make MARS memory allocation more robust"
	depends on MARS
	default y
	---help---
	Normally ON. Switch only off for systems having very low memory.

config MARS_LOGDIR
	string "absolute path to the logging directory"
	depends on MARS
	default "/mars"
	---help---
	Path to the directory where all MARS messages will reside.
	Usually this is equal to the global /mars directory.

	Logfiles and status files obey the following naming conventions:
		0.debug.log
		1.info.log
		2.warn.log
		3.error.log
		4.fatal.log
		5.total.log
	Logfiles must already exist in order to be appended.
	Logiles can be rotated by renaming them and creating
	a new empty file in place of the old one.

	Status files follow the same rules, but .log is replaced
	by .status, and they are created automatically. Their content
	is however limited to a few seconds or minutes.

config MARS_ROLLOVER_INTERVAL
	int "rollover time of logging status files (in seconds)"
	depends on MARS
	default 3
	---help---
	May influence the system load; dont use too low nubmers.

config MARS_SCAN_INTERVAL
	int "re-scanning of symlinks in /mars/ (in seconds)"
	depends on MARS
	default 5
	---help---
	May influence the system load; dont use too low nubmers.

config MARS_PROPAGATE_INTERVAL
	int "network propagation delay of changes in /mars/ (in seconds)"
	depends on MARS
	default 5
	---help---
	May influence the system load; dont use too low nubmers.

config MARS_SYNC_FLIP_INTERVAL
	int "interrpt sync by logfile update after (seconds)"
	depends on MARS
	default 60
	---help---
	0 = OFF. Normally ON.
	When disabled, application of logfiles may wait for
	a very time, until full sync has finished. As a
	consequence, your /mars/ filesystem may run out
	of space. When enabled, the applied logfiles can
	be deleted, freeing space on /mars/. Therefore,
	will usually want this. However, you may increase
	the time interval to increase throughput in favour
	of latency.

config MARS_NETIO_TIMEOUT
	int "timeout for remote IO operations (in seconds)"
	depends on MARS
	default 30
	---help---
	In case of network hangs, don't wait forever, but rather
	abort with -ENOTCONN
	when == 0, wait forever (may lead to hanging operations
	similar to NFS hard mounts)

config MARS_MEM_PREALLOC
	bool "avoid memory fragmentation by preallocation"
	depends on MARS
	default y
	---help---
	Normally ON. Switch off only for EXPERIMENTS!

config MARS_FAST_FULLSYNC
	bool "decrease network traffic at initial sync"
	depends on MARS
	default y
	---help---
	Normally ON.
	When on, both sides will read the data, compute a md5
	checksum, and compare them. Only in case the checksum
	mismatches, the data will be actually transferred over
	the network. This may increase the IO traffic in favour
	of network traffic. Usually it does no harm to re-read
	the same data twice (only in case of mismatches) over bio
	because RAID controllers will usually cache their data
	for some time. In case of buffered aio reads from filesystems,
	the data is cached by the kernel anyway.

config MARS_SHOW_CONNECTIONS
	bool "show connection status symlinks"
	depends on MARS
	default n
	---help---
	Normally OFF.

	When enabled, the status of all current network connections is
	written to /mars/resource-$resource/local-$host/connect-*
	showing the current status of all network connections by
	the following encoding:

	  -1 = connection is closed (not intended to start)
	   0 = connection is interrupted / not established
	   1 = connection is established at TCP level

	Warning! the symlinks are not deleted by the kernel. You have
	to cleanup old symlinks by yourself in userspace.

	When you forget the cleanup in regular intervals, you may
	end up with thoundands of symlinks accumulating in the
	/mars/resource-$resource/local-$host/ directory over a
	longer time.

	If unsure, say N here.

config MARS_LOGROT
	bool "allow logrotate during operation"
	depends on MARS
	default y
	---help---
	Normally ON. Switch off only for EXPERIMENTS!

config MARS_MIN_SPACE_4
	int "absolutely necessary free space in /mars/ (hard limit in GB)"
	depends on MARS
	default 2
	---help---
	HARDEST EMERGENCY LIMIT

	When free space in /mars/ drops under this limit,
	transaction logging to /mars/ will stop at all,
	even at all primary resources. All IO will directly go to the
	underlying raw devices. The transaction logfile sequence numbers
	will be disrupted, deliberately leaving holes in the sequence.

	This is a last-resort desperate action of the kernel.

	As a consequence, all secodaries will have no chance to
	replay at that gap, even if they got the logfiles.
	The secondaries will stop at the gap, left in an outdated,
	but logically consistent state.

	After the problem has been fixed, the secondaries must
	start a full-sync in order to continue replication at the
	recent state.

	This is the hardest measure the kernel can take in order
	to TRY to continue undisrupted operation at the primary side.

	In general, you should avoid such situations at the admin level.

	Please implement your own monitoring at	the admin level, which warns
	you and/or takes appropriate countermeasures much earlier.
	Never rely on this emergency feature!

config MARS_MIN_SPACE_3
	int "free space in /mars/ for primary logfiles (additional limit in GB)"
	depends on MARS
	default 2
	---help---
	MEDIUM EMERGENCY LIMIT

	When free space in /mars/ drops under
	MARS_MIN_SPACE_4 + MARS_MIN_SPACE_3,
	elder transaction logfiles will be deleted at primary resources.

	As a consequence, the secondaries may no longer be able to
	get a consecute series of copies of logfiles.
	As a result, they may get stuck somewhere inbetween at an
	outdated, but logically consistent state.

	This is a desperate action of the kernel.

	After the problem has been fixed, some secondaries may need to
	start a full-sync in order to continue replication at the
	recent state.

	In general, you should avoid such situations at the admin level.

	Please implement your own monitoring at	the admin level, which warns
	you and/or takes appropriate countermeasures much earlier.
	Never rely on this emergency feature!

config MARS_MIN_SPACE_2
	int "free space in /mars/ for secondary logfiles (additional limit in GB)"
	depends on MARS
	default 2
	---help---
	MEDIUM EMERGENCY LIMIT

	When free space in /mars/ drops under
	MARS_MIN_SPACE_4 + MARS_MIN_SPACE_3 + MARS_MIN_SPACE_2,
	elder transaction logfiles will be deleted at secondary resources.

	As a consequence, some local secondary resources
	may get stuck somewhere inbetween at an
	outdated, but logically consistent state.

	This is a desperate action of the kernel.

	After the problem has been fixed and the free space becomes
	larger than MARS_MIN_SPACE_4 + MARS_MIN_SPACE_3 + MARS_MIN_SPACE_2
	+ MARS_MIN_SPACE_2, the secondary tries to fetch the missing
	logfiles from the primary again.

	However, if the necessary logfiles have been deleted at the
	primary side in the meantime, this may fail.

	In general, you should avoid such situations at the admin level.

	Please implement your own monitoring at	the admin level, which warns
	you and/or takes appropriate countermeasures much earlier.
	Never rely on this emergency feature!

config MARS_MIN_SPACE_1
	int "free space in /mars/ for replication (additional limit in GB)"
	depends on MARS
	default 2
	---help---
	LOWEST EMERGENCY LIMIT

	When free space in /mars/ drops under MARS_MIN_SPACE_4
	+ MARS_MIN_SPACE_3 + MARS_MIN_SPACE_2 + MARS_MIN_SPACE_1,
	fetching of transaction logfiles will stop at local secondary
	resources.

	As a consequence, some local secondary resources
	may get stuck somewhere inbetween at an
	outdated, but logically consistent state.

	This is a desperate action of the kernel.

	After the problem has been fixed and the free space becomes
	larger than MARS_MIN_SPACE_4 + MARS_MIN_SPACE_3 + MARS_MIN_SPACE_2
	+ MARS_MIN_SPACE_2, the secondary will continue fetching its
	copy of logfiles from the primary side.

	In general, you should avoid such situations at the admin level.

	Please implement your own monitoring at	the admin level, which warns
	you and/or takes appropriate countermeasures much earlier.
	Never rely on this emergency feature!

config MARS_MIN_SPACE_0
	int "total space needed in /mars/ for (additional limit in GB)"
	depends on MARS
	default 12
	---help---
	Operational pre-requirement.

	In order to use MARS, the total space available in /mars/ must
	be  at least MARS_MIN_SPACE_4 + MARS_MIN_SPACE_3 + MARS_MIN_SPACE_2
	+ MARS_MIN_SPACE_1 + MARS_MIN_SPACE_0.

	If you cannot afford that amount of storage space, please use
	DRBD in place of MARS.

config MARS_LOGROT_AUTO
	int "automatic logrotate when logfile exceeds size (in GB)"
	depends on MARS_LOGROT
	default 32
	---help---
	You could switch this off by setting to 0. However, deletion
	of really huge logfiles can take several minutes, or even substantial
	fractions of hours (depending on the underlying filesystem).
	Thus it is highly recommended to limit the logfile size to some
	reasonable maximum size. Switch only off for experiments!

config MARS_PREFER_SIO
	bool "prefer sio bricks instead of aio"
	depends on MARS
	default n
	---help---
	Normally OFF for production systems.
	Only use as alternative for testing.