Re: Low traffic Ceph cluster with consumer SSD.

[Jesper Krogh <jesper@xxxxxxxx>]

On 25 Nov 2018, at 15.17, Vitaliy Filippov <vitalif@xxxxxxxxxx> wrote:

All disks (HDDs and SSDs) have cache and may lose non-transactional writes that are in-flight. However, any adequate disk handles fsync's (i.e SATA FLUSH CACHE commands). So transactional writes should never be lost, and in Ceph ALL writes are transactional - Ceph issues fsync's all the time. Another example is DBMS-es - they also issue an fsync when you COMMIT.

https://www.usenix.org/system/files/conference/fast13/fast13-final80.pdf

This may have changed since 2013, normal understanding is that cache need to be disabled to ensure that flushed are persistent, and disabling cache in ssd is either not adhered to by firmware or plummeting the write performance.

Which is why enterprise discs had power loss protection in terms of capacitors.

again any links/info telling otherwise is very welcome

Jesper

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