Re: software or hardware RAID? - Mailing list pgsql-general

On 3/23/19 11:51 AM, Rory Campbell-Lange wrote:
> On 23/03/19, Andy Colson (andy@squeakycode.net) wrote:
>> On 3/23/19 7:09 AM, Rory Campbell-Lange wrote:
>>> On 17/03/19, Rory Campbell-Lange (rory@campbell-lange.net) wrote:
> ...
>>>> We're buying some new Postgres servers with
>>>>
>>>>       2 x 240GB Intel SSD S4610 (RAID1 : system)
>>>>       4 x 960GB Intel SSD S4610 (RAID10 : db)
>>>>
>>>> We'll be using Postgres 11 on Debian.
>>>>
>>>> The MegaRAID 9271-8i with flash cache protection is available from our
>>>> provider. I think they may also have the 9361-8i which is 12Gb/s.
>>>>
>>>> Our current servers which use the LSI 9261 with SSDs and we don't see
>>>> any IO significant load as we are in RAM most of the time and the RAID
>>>> card seems to flatten out any IO spikes.
>>>>
>>>> We use MDRaid elsewhere but we've never used it for our databases
>>>> before.
> 
>>> Has anyone got any general comments on whether software RAID or an LSI card
>>> is preferable?
>>>
>>> We will be replicating load on an existing server, which has an LSI 9261 card.
>>> Below is some stats from sar showing a "heavy" period of load on vdisk sda
>>>
>>>     00:00:01  DEV     tps  rd_sec/s  wr_sec/s  avgrq-sz  avgqu-sz     await     svctm     %util
>>>     14:15:01  sda  112.82    643.09  14986.24    138.53      2.09     18.50      0.25      2.86
>>>     14:25:01  sda  108.52    270.17  15682.94    147.01      1.87     17.22      0.25      2.73
>>>     14:35:01  sda  107.96    178.25  14868.52    139.37      1.70     15.73      0.23      2.53
>>>     14:45:01  sda  150.97    748.94  16919.69    117.03      1.83     12.11      0.22      3.28
> 
>> I have run both software and hardware (though different than the card you listed), and had good success with both.
Incases where I had little money, just drop 6 drives into a md raid 10, and run happy for years and years.  I run
productionPG 11 on software raid 10 as we speek.
 
>>
>> I personally prefer software raid, for a few reasons:
>> 1) you'll probably be running on a batter backup anyway, so missing raid card battery isn't that much
>> 2) 100% compatible with any other hardware you wanna run.  Sucky thing about hardware card is your on that one
forever.
>> 3) tooling is much better and simpler.  I really hate the crappy bios raid screen.  I never know if adding an HD to
anexiting raid will wipe it or maintain it.
 
>> 4) I setup smartctl to watch and report on drives.  Even a 50% chance it detects before failure is a net benefit.
Youcant always to that through hardware raid
 
>>
>> You can always start with software raid, see how it runs for a while, then buy hardware raid if its not working
out.
> 
> Thanks very much for the comments, Andy.
> 
> If money was no object, would you choose a fancy hardware RAID card?
> 
> You are right that the SSDs we are purchasing have enough cache + power to not need a BBU, and I agree that the
managementtools for software raid are much more convenient.
 
> 
> Rory
> 


That's a tough question.  I don't even have SSD's yet.  I can't say what performance is like on HW Raid SSD vs SW Raid
SSD. If money where no object, and I wanted performance over all else, I'd benchmark both.
 

If usability were >= performance, I'd go with extra ram, and SW Raid SSD.  And a BMW. :-)

-Andy