[DRBD-user] disk-barrier

Roberto Fastec roberto.fastec at gmail.com
Mon Oct 27 18:00:31 CET 2014

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

Dear friends

One kind clarification

the manual of 8.4 says about disk-barriers

Use disk barriers to make sure that requests are written to disk in
the right order. Barriers ensure that all requests submitted before a
barrier make it to the disk before any requests submitted after the
barrier. This is implemented using 'tagged command queuing' on SCSI
devices and 'native command queuing' on SATA devices."

and at the end of the disk -barrier it says

"Only some devices and device stacks support this method. The device
mapper (LVM) only supports barriers in some configurations."

this last sentence confuses me a bit, since in XenServer it is used
LVM and I'm using it

and at the very end of the section it says

"Depending on the I/O stack, write requests can be reordered, and they
can be submitted in a different order on different cluster nodes. This
can result in data loss or corruption. Therefore, turning off all
three methods of controlling write ordering is strongly discouraged. "

Ok. So what?

What it is best to do with a XenServer environment with LVM on SATA disks?

Thank you for hinting


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