From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin ESTRABAUD Subject: Re: {Possible Spam} RE: stripe_cache_active always 0 Date: Thu, 07 Jan 2016 17:53:47 +0000 Message-ID: <568EA62B.80103@mpstor.com> References: <568DD6E6.6070107@websitemanagers.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Robert Kierski , Adam Goryachev , "linux-raid@vger.kernel.org" List-Id: linux-raid.ids On 07/01/16 16:34, Robert Kierski wrote: > Adam, > > stripe_cache_active is the value to indicate how many pages are curre= ntly in use in the stripe cache. I could be wrong about this... but I = don=E2=80=99t think you can disable the stripe cache. You can shrink i= t to an unreasonable size, but the minimum you can set stripe_cache_siz= e to is 17 (pages). > > Having said that, it may be that your RAID isn't using the stripe cac= he or that you're not checking the value frequently enough to see strip= e cache activity. > > A file system that is properly tuned, and doing buffered IO will like= ly reduce the stripe cache usage. The stripe cache is basically where = data gets put when the RAID is doing partial stripe IO's, calculating p= arity, or waiting for slow devices to complete their IO's. It's not in= tended to be yet another level of cache, so it gets purged when the RAI= D is done with it. So, unlike other caches that will hold onto data un= til there is memory pressure, the stripe cache is more likely to be emp= ty. > > As far as adjusting stripe_cache_size... The stripe cache is dynamica= lly allocated. It won't save any RAM by decreasing stripe_cache_size. = Decreasing it too much will negatively impact performance as it's more= likely you'll do Read-Modify-Write's when doing partial stripe writes. > I find that tuning it a bit higher (but not too high) has a very=20 positive impact on rebuild times (where we are therefore building=20 stripes). I can't remember exactly the values but we were setting it to= =20 256 or 512 or even 1024 while building RAID5 or 6 with positive results= =2E Regards, Ben. > Bob Kierski > Senior Storage Performance Engineer > Cray Inc. > 380 Jackson Street > Suite 210 > St. Paul, MN 55101 > Tele: 651-967-9590 > Fax: 651-605-9001 > Cell: 651-890-7461 > > N=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BDr=EF=BF=BD=EF=BF=BDy=EF= =BF=BD=EF=BF=BD=EF=BF=BDb=EF=BF=BDX=EF=BF=BD=EF=BF=BD=C7=A7v=EF=BF=BD^=EF= =BF=BD)=DE=BA{.n=EF=BF=BD+=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD{=EF=BF=BD= =EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD{ay=EF=BF=BD=1D=CA=87=DA=99=EF=BF=BD= ,j=07=EF=BF=BD=EF=BF=BDf=EF=BF=BD=EF=BF=BD=EF=BF=BDh=EF=BF=BD=EF=BF=BD=EF= =BF=BDz=EF=BF=BD=1E=EF=BF=BDw=EF=BF=BD=EF=BF=BD=EF=BF=BD=0C=EF=BF=BD=EF= =BF=BD=EF=BF=BDj:+v=EF=BF=BD=EF=BF=BD=EF=BF=BDw=EF=BF=BDj=EF=BF=BDm=EF=BF= =BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=07=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BDzZ= +=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=EF=BF=BD=DD=A2j"=EF=BF=BD=EF=BF=BD= !tml=3D > -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html