It's old and incomplete information, website already has a more complete FAQ Cc: Christophe Varoqui <christophe.varoqui@xxxxxxxxxxx> Cc: device-mapper development <dm-devel@xxxxxxxxxx> Signed-off-by: Xose Vazquez Perez <xose.vazquez@xxxxxxxxx> --- FAQ | 97 --------------------------------------------------------------------- 1 file changed, 97 deletions(-) delete mode 100644 FAQ diff --git a/FAQ b/FAQ deleted file mode 100644 index 040f807..0000000 --- a/FAQ +++ /dev/null @@ -1,97 +0,0 @@ -More at http://christophe.varoqui.free.fr/faq.html -See also http://christophe.varoqui.free.fr/usage.html - -1. How to set up System-on-multipath ? -====================================== - -prerequisite : udev and multipath-tools installed - -here are the steps on a Debian SID system : - -* add dm-mpath and dm-multipath to /etc/mkinitrd/modules -* copy $tools_dir/multipath/0[12]_* to /etc/mkinitrd/scripts -* define a friendly alias for your multipathed root disk - (in /etc/multipath.conf). Example : "system" -* enable busybox in /etc/mkinitrd/mkinitrd.conf and set ROOT - to any valid block-device (but not a /dev/dm-* one, due to - an mkintrd misbelief that all dm-* are managed by LVM2) -* run mkinitrd -* in /boot/grub/menu.lst, define the root= kernel parameter - Example : root=/dev/system1 -* modify /etc/fstab to reference /dev/system* partitions - -At reboot, you should see some info like : - -path /dev/sda : multipath system -... -gpt: 0 slices -dos: 5 slices -reduced size of partition #2 to 63 -Added system1 : 0 70685937 linear /dev/system 63 -Added system2 : 0 63 linear /dev/system 7068600 -Added system5 : 0 995967 linear /dev/system 70686063 -... - -2. How does it compare to commercial product XXX ? -================================================== - -Here are a few distinctive features : - -* you can mix HBA models, even different vendors, different speed ... -* you can mix storage controllers on your SAN, and access them all, applying - different path grouping policy -* completely event-driven model : no administration burden if you accept the - default behaviours -* extensible : you can plug your own policies if the available ones don't fill - your needs -* supports root FS on multipathed SAN -* free, open-source software - -3. LVM2 doesn't see my multipathed devices as PV, what's up ? -============================================================= - -By default, lvm2 does not consider device-mapper block devices (such as a -dm-crypt device) for use as physical volumes. - -In order to use a dm-crypt device as an lvm2 pv, add this line to the -devices block in /etc/lvm/lvm.conf: - -types = [ "device-mapper", 16 ] - -If /etc/lvm/lvm.conf does not exist, you can create one based on your -current/default config like so: - -lvm dumpconfig > /etc/lvm/lvm.conf - -(tip from Christophe Saout) - -4. I see a lot of "io_setup failed" message using the directio checker -====================================================================== - -The directio path checker makes use of the asynchronous I/O API (aio) provided -by modern Linux systems. Asynchronous I/O allows an application to submit I/O -requests asynchronously and be notified later of their completion status. To -allow this, we must allocate an asynchronous I/O context (an object of type -aio_context_t) and this task is handled by the io_setup system call. - -A system wide limit on the number of AIO contexts that may be active -simultaneously is imposed via the aio-max-nr sysctl parameter. - -Once this limit has been reached further calls to io_setup will fail with the -error number EAGAIN leading to the "io_setup failed" messages seen for e.g. when -running "multipath -ll". - -To avoid this problem the number of available aio contexts should be increased -by setting the aio-max-nr parameter. This can be set on a one-time basis via the -/proc file system, for e.g.: - - # echo 131072 > /proc/sys/fs/aio-max-nr - -Doubles the number of available contexts from the default value of 65536. - -To make this setting persistent a line may be added to /etc/sysctl.conf: - - fs.aio-max-nr = 131072 - -Consult appropriate application and operating system tuning recommendations for -guidance on appropriate values for this parameter. -- 2.5.5 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
