Re: Intel 710 pgbench write latencies

On 2011-11-02 16:06, Magnus Hagander wrote:
> On Wed, Nov 2, 2011 at 16:04, Yeb Havinga<yebhavinga(at)gmail(dot)com> wrote:
>> On 2011-11-02 15:06, Kevin Grittner wrote:
>>> Yeb Havinga<yebhavinga(at)gmail(dot)com> wrote:
>>>
>>>> I'm now contemplating not using the 710 at all. Why should I not
>>>> buy two 6Gbps SSDs without supercap (e.g. Intel 510 and OCZ Vertex
>>>> 3 Max IOPS) with a IO controller+BBU?
>>> Wouldn't the data be subject to loss between the time the IO
>>> controller writes to the SSD and the time it makes it from buffers
>>> to flash RAM?
>> Good question. My guess would be no, if the raid controller does
>> 'write-throughs' on the attached disks, and the SSD's don't lie about when
>> they've written to RAM.
> Doesn't most SSDs without supercaps lie about the writes, though?
>

I happened to have a Vertex 3, no supercap, available to test this with
diskchecker. On a ext4 filesystem (just mounted with noatime, not
barriers=off), this happenend:

# /root/diskchecker.pl -s 192.168.73.1 verify testfile
verifying: 0.00%
verifying: 30.67%
verifying: 78.97%
verifying: 100.00%
Total errors: 0

So I guess that's about as much as I can test without actually hooking
it behind a hardware controller and test that. I will soon test the
3ware 9750 with Vertex 3 and Intel 510 - both in the 3ware's ssd
compatibility list.

More info from testing software raid 1:
- with lvm mirroring, discards / trim go through to the disks. This is
where the Intel is fast enough, but the vertex 2 pro is busy for ~ 10
seconds.

-- Yeb