On 10/02/15 20:40, Thomas Güttler wrote:
Hi,
does the lack of a battery backed cache in Ceph introduce any
disadvantages?
We use PostgreSQL and our servers have UPS.
But I want to survive a power outage, although it is unlikely. But "hope
is not an option ..."
You can certainly make use of adapter cards that have a battery backed
cache with Ceph - either using RAID as usual or creating arrays of "RAID
0 of 1 disk" that enable you to use the nice battery backed cache +
writeback options on the card and still have a "1 osd mapped to 1 disk"
topology.
Without such cards it is still quite possible to have a power loss safe
setup. These days (with reasonably modern 3.* kernels) using SATA or SAS
plus mount options that do *not* disable write barriers will leave you
with a consistent, safe state in the advent of power loss. You might
want to test your SATA disk of choice to be sure, but SAS should be safe!
Cheers
Mark
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