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i’m operating a Leap 42.1 system with a Data Storage based on LVM using a VG based on a Adaptec 2405 RAID1 6TB Array and a Samsung M2 SSD 950 Pro as caching device (DM-Cache). Using the MQ caching policy i can operate the device and i was able to play arround with some parameters which are increaring but also decreasing the performance. Mostly i see that the default values (random_threshold=4 sequential_threshold=512 read_promote_adjustment=4 write_promote_adjustment=8) bringing the most performance benefit especially for a MariaDB DB in a VM executed from NFS and other small file fun without negative impact on transfer of large files (some other, more aggressive settings had huge negative impact on large files transfers, e.g just 50MB/s over network) .
- I wonder, i’ve understood here that SMQ is the default policy. But after first activation of the caching device on leap with default values and without caching policy definition i saw, that MQ is enabled. Why, when SMQ is default?
- After many experiments with the created cache using some parameters i’ve decided to switch to SMQ for deeper testing. I’ve tried to switch to SMQ using *lvchange --cachepolicy smq array2/media *but this hasn’t been accepted giving a *device-mapper: reload ioctl on (252:3) failed: Invalid argument *as output and the dmesg record *device-mapper: cache-policy: unknown policy type. *Enabling the MQ policy using this way is working, also varying other parameters so i assume that i’ve haven’t misstyped the command.
Do anybody know why i can not activate SMQ on Lead 42.1 as decribed on many places in the Internet? It also wonders me why this seems to be default (kernel documentation) but for suse it is MQ. Has anybody an answer on my questions?