On 21/04/11 05:50, Ryan Wagoner wrote:

On Wed, Apr 20, 2011 at 7:24 AM, David Brown[off-list ref]  wrote:

quoted

Pros for hardware raid:

+ It can have battery backup (I don't have one at the moment - I have an
excellent UPS for the whole system).
+ Rebuilds will be handled automatically by just adding new disks
+ The card supports online resizing and reshaping
+ It looks like the card supports caching with an SSD
+ The card supports snapshots of the virtual drives

Unless the card allows you to enable the write cache without the
backup battery you will not see the real performance of the card. This
option is normally locked out to prevent data loss in case the system
crashes, power is pulled, etc. An external UPS will not protect in all
cases if you enable the write back cache without battery.

The write cache is allowed without the battery, but disabled by default.

I agree that even with an UPS there is still a risk - I guess that's why 
it is disabled.  But the risk is pretty minimal for me - there is no 
realistic chance of the power plug being pulled, for example.  Other 
risks do exist - the power supply on the server may fail, the UPS may 
fail, etc.  In the end there are /always/ risks - even with a battery on 
the raid card, it won't protect against everything.  All I can do is 
reduce the risks to a realistic minimum while keeping good performance 
and features (and sensible cost!), and make sure I've got good backups 
of everything.

I have systems with both software raid and hardware raid. If the
budget allows I tend to go the hardware raid route. When buying a
Dell, HP, etc server with hardware raid you end up with a complete
package. The enclosure, card, and server monitoring software make it
easy to manage and visually see which drive has failed.

Ryan
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