| From: | Craig Ringer <craig(at)postnewspapers(dot)com(dot)au> |
|---|---|
| To: | Andy <angelflow(at)yahoo(dot)com> |
| Cc: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: BBU still needed with SSD? |
| Date: | 2011-07-18 02:30:20 |
| Message-ID: | 4E239ABC.4020204@postnewspapers.com.au |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-performance |
On 18/07/2011 9:43 AM, Andy wrote:
> Hi,
>
> 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.
> 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?
>
You don't need write-back caching for fsync() performance if your SSDs
have big enough caches. I don't know enough to say whether there are
other benefits to having them on a BBU HW raid controller or whether SW
RAID is fine.
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