Power outage, data loss?

[markus]

Hi,

in the documentation and here in the forum I could - of course - find the strong advice never to use a RAID controller with write cache enabled and without a BBU. That's obvious.

I could also find out that DSS uses "a few MB" of RAM for caching in block IO mode, and all available memory for read and write caching in file IO mode.

Does this mean that an unclean shutdown of a DSS server could result in really serious data loss, even if I use a BBU for the RAID controller?

[To-M]

If is this is a production server I would recommend using a UPS as well to prevent this possibility. If there is IO being written during an unclean shutdown then you will most likely have loss of data.

[markus]

Thank you very much.

Hmm, even it is a less critical or non-production system: downtime might be acceptable, data loss never. That's why probably none of your customers is using a RAID 0 array

So a UPS is an essential part of any open-e installation. I would prefer if this would be much more highlighted on your website, especially for the "NAS in 10 minutes" kind of customers.

There are even hardware suppliers offering complete server configurations based on open-e software and do not even offer any UPS system listed on your compatibility matrix...

[Robotbeat]

Do not the iscsi target settings have an option for write-back or write-through cache? If this isn't for the system memory, then what is it for? If write-through is enabled, doesn't this, by default, prevent data corruption in case of a power outage (since the write wouldn't be acknowledged until it's actually on disk)?

[To-M]

Yes that is true - but I can tell you from one customers experience as he will tell you otherwise and he wished he invested even on a cheap $250 UPS when they had a power hit during a very critical time of file transfer the power hit took out the system including the USB module. So Markus - I will always recommend a UPS and this is my opinion as well as this customer not the suppliers.