I have a server with a UPS, life on battery is around 20-30mins, the server has a 2405/128MB without BBU, I am just confused as to do I really need a BBU card?
Surely if the UPS is working, during a power failure, t should allowed plenty of time for the cache to write through ? or am I missing something ? I don't really want to spent a fortune on a card just for the sake of a BBU, the applications are more towards read,rather than write on a ratio of around 5-1, is it really such a risk to work without a BBU even though theres a good UPS ?
RAID Battery and UPS
bburaidups
Related Topic
- Improving RAID performance
- APC UPS replace battery light and apcupsd reporting “replace battery”
- Non-volatile cache RAID controllers: what kind of protection is there against NVCACHE failure
- Change the UPS battery while it’s powered on
- How to disable UPS energy_saving with NUT
- LSI iBBU07 troubleshoot: BBU not detected
- Does the RAID BBU battery charge while server is powered off
Best Answer
Although this covers some of ground as the duplicate August proposed, I'm not going to second closing this question as the answers there are rather poor.
A BBU disk controller does indeed provide protection against a power outage - but it also (in conjunction with a journalling or log-structured filesystem) provides protection against server OS crashes and disk hardware failures - which your UPS doesn't. It's not the only way to address the availabity problem - the other approach is to duplicate the server and UPS and disk and use appropriate clustering tools.
Further, with a larger, non-volatile cache, it allows the the OS to securely offload write operations to the disk much faster - the OS doesn't have to hang around as long waiting for the disk subsystem to confirm that the write has committed. Having a larger buffer gives the thing which writes sectors to the disk (n the this case the disk controller) much more scope for scheduling the operations in order to optimize them, giving a further performance benefit. And if you're using SSDs then you get a bit benefit from running a large marshalling buffer in terms of reduced write wear.
Really? I would say this is rather write heavy.
While the last time I looked, a low end UPS was still cheaper than a basic BBU disk controller, the latter can had from around £100 ($150). You just need to hunt around a bit. I would much rather have a BBU disk controller and cheap disks than expensive disks and no BBU - both for performance and availability.