software raid + fs -- performance

[Papadogiannakis Vagelis]

On Wed, 19 Jun 2002 01:58:45 +0300
V13 <v13 at priest.com> wrote:

>  Thelo hints & tips pano sto eksis:
> 
>  Exo 2 diskoys... Pros to paron toys exo balei na doylevoyn me raid0, alla den 
> tha peiraze na einai kai raid1 (ta alla ypotheto oti den ta syzitame stin 
> periptosi ayti). To zitoymeno einai oso to dynaton megalyteri taxytita gia 
> xrisi apo postgreSQL. H basi ginetai arketa megali (merika GB) kai sxedon ola 
> ta queries ginontai me basi indexes. Ayto simenei oti o xronos spatalatai 
> kyrios se seek kai oxi se read/write. Oi diskoi einai scsi me 30+ MB/s read 
> apo tin epifaneia toy diskoy, eno me to raid exo ftasei ta 60+ MB/s write. 
> 
>  Exo dokimasei ext3(me -T largefile kai -T largefile4), raiserfs kai xfs kai 
> exo xrisimopoihsei san chunk-size sto raid, times apo 64K mexri 2MB. Par'ola 
> ayta den eida kapia aisthiti diafora kai tyxainoyn stigmes opoy to vmstat 
> dixnei bi (read apo diskoys) mikroteres apo 1.5MB/s (kai ayto einai kai to 
> 'bottleneck' tis periptosis') eno oi diskoi doylevoyn san treloi, me ta 
> lampakia toys na anaboyn synexeia kai na kanoyn 'arketi' fasaria. Epeksa ligo 
> me to stripe toy ext3, alla kai pali den ebgala akri.
> 
>  Exo kataliksei sto xfs, giati ap'oti eida ta paei kalytera me megala arxeia 
> (to olo 'partition' apoteleitai apo ligotero apo 200 arxeia kai den yparxoyn 
> prooptikes na ayksithoyn) kai epidi moy fenetai oti den kathysterei to 
> systima otan kanei flush tin cache (antitheta me ta alla 2). 
> 
>  Par'ola ayta oti benchmark katafera na bro sto web, exoyn na kanoyn me polla 
> arxeia, h me syriaki xrisi megalon arxeion.... 
> 
>  Opiadipote protasi/empeiria kalodexoymeni...

apo tin prosopiki mou empeiria, (kai exontas paiksi kai ego me chunk sizes, filesystems, k.lp.) to mono pou katafera itan na... min do ousiastiki diafora. Afto pou xreiazetai pragmatika einia i kali sxediasi tis db kai ta katalila indexes ekei pou prepei. An pisteveis oti i vasi sou den sikonei allo optimization kai pali den eisai efxaristimenos apo tin apodosi, isos na prepei na pas se HW ilopoihsh raid (an pragmatika se kaiei kai exeis na doseis kapoia fraga parapano). Isos an mporouses na pareis allo ena disko na kaneis stripeset, opou i taxitita read einai safos kaliteri (propantos se scsi). Se afti tin periptosi to write vevaia einai pio argo, alla opos eipes kai esi den se endiaferei kai toso.

Isos an evazes perissoteri mnimi?


>  Na shmeiothei oti den me niazei sxedon katholoy h taxytita toy write.. Mono 
> sto read/seek thelo taxytita, gia ayto kai dialeksa raid0.
> 
> <<V13>>




--
Vagelis Papadogiannakis
http://www.wise.gr
papas at wise.gr