I'm using Ceph on Ubuntu 16.04 on Dell R730xd servers. A recent [1] update to the PERC firmware disabled the disk write cache by default which made a noticable difference to the latency on my disks (spinning disks, not SSD) - by as much as a factor of 10. For reference their change list says: "Changes default value of drive cache for 6 Gbps SATA drive to disabled. This is to align with the industry for SATA drives. This may result in a performance degradation especially in non-Raid mode. You must perform an AC reboot to see existing configurations change." It's fairly straightforward to re-enable the cache either in the PERC BIOS, or by using hdparm, and doing so returns the latency back to what it was before. Checking the Ceph documentation I can see that older versions [2] recommended disabling the write cache for older kernels. But given I'm using a newer kernel, and there's no mention of this in the Luminous docs, is it safe to assume it's ok to enable the disk write cache now? If it makes a difference, I'm using a mixture of filestore and bluestore OSDs - migration is still ongoing. Thanks, Tim. [1] - https://www.dell.com/support/home/uk/en/ukdhs1/Drivers/DriversDetails?driverId=8WK8N [2] - http://docs.ceph.com/docs/jewel/rados/configuration/filesystem-recommendations/ -- Tim Bishop http://www.bishnet.net/tim/ PGP Key: 0x6C226B37FDF38D55 _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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