Re: BBU still needed with SSD?

On Sun, Jul 17, 2011 at 7:30 PM, Craig Ringer
<craig@postnewspapers.com.au> wrote:
> On 18/07/2011 9:43 AM, Andy wrote:
>> Is BBU still needed with SSD?
>
> You *need* an SSD with a supercapacitor or on-board battery backup for its
> cache. Otherwise you *will* lose data.
>
> Consumer SSDs are like a hard disk attached to a RAID controller with
> write-back caching enabled and no BBU. In other words: designed to eat your
> data.

No you don't.  Greg Smith pulled the power on a Intel 320 series drive
without suffering any data loss thanks to the 6 regular old caps it
has.  Look for his post in a long thread titled "Intel SSDs that may
not suck".

>> In this case is BBU still needed? If I put 2 SSD in software RAID 1, would
>> that be any slower than 2 SSD in HW RAID 1 with BBU? What are the pros and
>> cons?

What will perform better will vary greatly depending on the exact
SSDs, rotating disks, RAID BBU controller and application.  But
certainly a couple of Intel 320s in RAID1 seem to be an inexpensive
way of getting very good performance while maintaining reliability.

-Dave