hdd + ssd

hdd + ssd

[krautus]

Hello I'm trying to understand why and how to add one or more SSD (as a cache drive / keeping xfs log)
to a traditional spinning xfs storage volume.
I mean: which data will go to the ssd ? Inodes and dentries will go to the ssd ?
Will the _read_ performance increase ?

In general I'm looking to increase (cache) the reading performance of folders with a lot of small files (emails),
for email servers.

Feel free to let me rtfm :)
I'd gladly study the documentation / articles / benchmarks but my google-fu isn't in best shape.

Thank you,
Mike
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Re: hdd + ssd

[Eric Sandeen]

On 10/22/15 1:23 PM, krautus@kr916.org wrote:
> Hello I'm trying to understand why and how to add one or more SSD (as a cache drive / keeping xfs log)
> to a traditional spinning xfs storage volume.
> I mean: which data will go to the ssd ? Inodes and dentries will go to the ssd ?
> Will the _read_ performance increase ?

You might want to look into something like dm-cache
https://en.wikipedia.org/wiki/Dm-cache

(TBH, I've not used it before, so grains of salt apply for your usecase).

Putting the log on an ssd is not likely to be the solution you want;
it certainly won't speed up reads.

-Eric

> In general I'm looking to increase (cache) the reading performance of folders with a lot of small files (emails),
> for email servers.
> 
> Feel free to let me rtfm :)
> I'd gladly study the documentation / articles / benchmarks but my google-fu isn't in best shape.
> 
> Thank you,
> Mike
> _______________________________________________
> xfs mailing list
> xfs@oss.sgi.com
> http://oss.sgi.com/mailman/listinfo/xfs
> 

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Re: hdd + ssd

[Emmanuel Florac]

Le Thu, 22 Oct 2015 20:23:24 +0200
"krautus@kr916.org" <krautus@kr916.org> écrivait:

> Hello I'm trying to understand why and how to add one or more SSD (as
> a cache drive / keeping xfs log) to a traditional spinning xfs
> storage volume. I mean: which data will go to the ssd ? Inodes and
> dentries will go to the ssd ? Will the _read_ performance increase ?
> 
> In general I'm looking to increase (cache) the reading performance of
> folders with a lot of small files (emails), for email servers.
> 
> Feel free to let me rtfm :)
> I'd gladly study the documentation / articles / benchmarks but my
> google-fu isn't in best shape.

You've got several options, some integrated with the kernel: dm-cache
and bcache, some available as additional tools: flashcache and
EnhanceIO.

YMMV, but here's my take:

 * flashcache being a facebook internal dev, probably is the most
   largely deployed one. It's clearly production-ready.

 * EnhanceIO works fine but I haven't tested it thoroughly. It adds no
   signature to the drives so it can be added to existing filesystems
   (flashcache and bcache need reformatting). However that means that
   bad thing may happen if you're careless -- it's clearly targeted at
   always-on servers.

 * bcache works fine but the latest fixes haven't been backported, so
   you should probably use it only with latest (4.2, 4.3) kernels. It's
   not very mature yet but it's *friggin' fast*.

 * dm-cache is the easiest to set-up with the lvmcache command (if your
   distro is recent enough of course). Like very very easy. It's
   unfortunately the slowest of the pack, apparently. Doesn't need
   reformatting IF your existing FS already lives in a LV. 

-- 
------------------------------------------------------------------------
Emmanuel Florac     |   Direction technique
                    |   Intellique
                    |	<eflorac@intellique.com>
                    |   +33 1 78 94 84 02
------------------------------------------------------------------------

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Re: hdd + ssd

[Stefan Ring]

On Fri, Oct 23, 2015 at 1:48 PM, Emmanuel Florac <eflorac@intellique.com> wrote:
> YMMV, but here's my take:
>
>  * flashcache being a facebook internal dev, probably is the most
>    largely deployed one. It's clearly production-ready.
>
>  * EnhanceIO works fine but I haven't tested it thoroughly. It adds no
>    signature to the drives so it can be added to existing filesystems
>    (flashcache and bcache need reformatting). However that means that
>    bad thing may happen if you're careless -- it's clearly targeted at
>    always-on servers.
>
>  * bcache works fine but the latest fixes haven't been backported, so
>    you should probably use it only with latest (4.2, 4.3) kernels. It's
>    not very mature yet but it's *friggin' fast*.
>
>  * dm-cache is the easiest to set-up with the lvmcache command (if your
>    distro is recent enough of course). Like very very easy. It's
>    unfortunately the slowest of the pack, apparently. Doesn't need
>    reformatting IF your existing FS already lives in a LV.

Very good summary, thanks! Do you also happen to know if all of these
retain cache contents across reboots?

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Re: hdd + ssd

[krautus]

Thank you all for the suggestions!
I'll report back my progress, will take a while .. :)

Bye and have a nice week-end,
Mike

On Fri, 23 Oct 2015 23:34:00 +0200
Stefan Ring <stefanrin@gmail.com> wrote:

> On Fri, Oct 23, 2015 at 1:48 PM, Emmanuel Florac <eflorac@intellique.com> wrote:
> > YMMV, but here's my take:
> >
> >  * flashcache being a facebook internal dev, probably is the most
> >    largely deployed one. It's clearly production-ready.
> >
> >  * EnhanceIO works fine but I haven't tested it thoroughly. It adds no
> >    signature to the drives so it can be added to existing filesystems
> >    (flashcache and bcache need reformatting). However that means that
> >    bad thing may happen if you're careless -- it's clearly targeted at
> >    always-on servers.
> >
> >  * bcache works fine but the latest fixes haven't been backported, so
> >    you should probably use it only with latest (4.2, 4.3) kernels. It's
> >    not very mature yet but it's *friggin' fast*.
> >
> >  * dm-cache is the easiest to set-up with the lvmcache command (if your
> >    distro is recent enough of course). Like very very easy. It's
> >    unfortunately the slowest of the pack, apparently. Doesn't need
> >    reformatting IF your existing FS already lives in a LV.
> 
> Very good summary, thanks! Do you also happen to know if all of these
> retain cache contents across reboots?
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Re: hdd + ssd

[Emmanuel Florac]

Le Fri, 23 Oct 2015 23:34:00 +0200
Stefan Ring <stefanrin@gmail.com> écrivait:

> Very good summary, thanks! Do you also happen to know if all of these
> retain cache contents across reboots?

Yes, they retain cache contents across reboots.

-- 
------------------------------------------------------------------------
Emmanuel Florac     |   Direction technique
                    |   Intellique
                    |	<eflorac@intellique.com>
                    |   +33 1 78 94 84 02
------------------------------------------------------------------------

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