UNIX for Dummies Questions & Answers

After searching and finding the link to the A1000 pdf ( http://192.18.99.138/805-7147/805-7147.pdf ) my questions are:

1) I have a battery failure on a A1000. I know that caching is disabled and it reports to see log. After reading the manual I have learned that the battery is a data-cache hold up battery in the hardware raid controller board(holding data memory for up to 3 days). Can someone explain what is meant by "data-cache" and what is it's benefits if the power fails?

I need to explain why/if it is so important to take down server(and order a new battery) and replaced the failed battery.

Does it need to be replaced?

Cache is a holding area. When the computer writes to a disk, the RAID can acknowledge the write as soon as the data has arrived in cache. This makes disk writes seem to be much faster. But you probably want that data to actually get written to the disk. (A cache will delay for awhile in case the data is written again. That way multiple disk writes actually become a single write.) But if you lose power, the actual disks stop spinning. Now you need to preserve the data until power is restored. That's where the battery comes in.

So far, we've talked about write-behind. But cache is also used for read-ahead. The RAID is paying attention to which data the computer wants and tries to guess which read may occur in the future. If a disk goes idle, it will issue the reads to have the data in the cache ready for a read to occur.

This is big performance boost, and without the cache performance drops.

Even if I didn't care about disk i/o performance. I would replace the battery. The code in firmware of the RAID may have bugs. And they probably don't test degraded mode as thoroughly as it's normal mode. Degraded hardware always makes me nervous.

Thanks for the explanation....good stuff. I will try to order a new one.