And you Hardforumer, what do you think about this trick ?
Its not a trick, its a way to improve performance with the danger of data-loss on power-loss.
In extreme, you may loose about last 5s of data that are confirmed to be on disk prior power-loss.
If there are no writes in the last 5s, you have no data loss. If it was a transaction on a VM it may become corrupted.
If you have dependend financial transactions, your data may be inconsistent.
If you want to have it cheap with max performance and not too much danger, disable sync and add a UPS
The problem:
ZFS usually collects small async random writes in RAM and flush them in one large sequential write after a few seconds.
This can be more than 10x faster than small sync writes without a dedicated log device.
A slow log device can improve but only a little. You need very low latency and best write performance to achieve similar
values like with sync=disable. I have not yet seen or heard of a SSD than can really improve things when compared to
sync=disable or a RAM based log device. Thats a pity because you need only a few GB. You may look at a cheaper alternative
to a Zeus od DDRdrive disk. like Acard RAM based disks.
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