[CentOS] SSD support in C5 and C6

Fri Jul 19 21:04:47 UTC 2013
Wade Hampton <wadehamptoniv at gmail.com>

Thanks for the feedback.

Sounds like all this needs to be merged into a wiki?

Couple of take-aways:
- options will depend on the drive
  -- cheap drives, be more conservative with options including
     turning write-cache off
  -- provisioning depends on how much mfg reserves
- better options are available for CentOS 6
- kernel scheduler, swap, and /tmp changes might help
  for some use cases -- test and determine if they will help
  (e.g., if your system processes data and creates a lot of files
   in /tmp for processing, putting /tmp in RAM might help)


1)  Determine your use case
2)  Determine the type of drive you need and any items
     specific to the drive (reserved space, TRIM, big caps)
3)  Use newer Linux systems (CentOS 6, later UBUNTU, RHEL, Fedora)
     if you can -- and use EXT4 with trim enabled (if drive supports it)
4)  Test
5)  Deploy

Cheers,
--
Wade Hampton


On Fri, Jul 19, 2013 at 4:07 PM, Gordon Messmer <gordon.messmer at gmail.com>wrote:

> On 07/19/2013 11:21 AM, John R Pierce wrote:
> > On 7/19/2013 11:07 AM, Gordon Messmer wrote:
> >>> >>- under provision (only use 60-75% of drive, leave unallocated space)
> >> >That only applies to some drives, probably not current generation
> hardware.
> >> >
> > it applies to all SSDs.  they NEED to do write block remapping, if they
> > don't have free space, its much much less efficient..
>
> Well, maybe.
>
> The important factor is how much the manufacturer has over-provisioned
> the storage.  Performance targeted drives are going to have a large
> chunk of storage hidden from the OS in order to support block remapping
> functions.  Drives that are sold at a lower cost are often going to
> provide less reserved storage for that purpose.
>
> So, my point is that if you're buying good drives, you probably don't
> need to leave unpartitioned space because there's already a big chunk of
> space that's not even visible to the OS.
>
> Here are a couple of articles on the topic:
>
>
> http://www.edn.com/design/systems-design/4404566/Understanding-SSD-over-provisioning
> http://www.anandtech.com/show/6489/playing-with-op
>
> Anand's tests indicate that there's not really a difference between
> cells reserved by the manufacturer and cells in unpartitioned space on
> the drive.  If your manufacturer left less space reserved, you can
> probably boost performance by reserving space yourself by leaving it
> unpartitioned.
>
> There are diminishing returns, so if the manufacturer did reserve
> sufficient space, you won't get much performance benefit from leaving
> additional space unallocated.
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