Thank You, this is exactly what I need to understand.



http://stackoverflow.com/questions/5055859/how-are-the-o-sync-and-o-direct-flags-in-open2-different-alike


Gesendet: Mittwoch, 06. März 2013 um 20:51 Uhr
Von: PV <pv2pv@pochta.ru>
An: aoetools-discuss@lists.sourceforge.net
Betreff: Re: [Aoetools-discuss] Wr­ite-through cache
Thank You and yangyuanzhi@gmail.com !
'man vblade' has answer .. but I had not understand what is
"O_DIRECT and O_SYNC mode for accessing  the  underlying block device"
Let me try ...

Срд 06 Мар 2013 12:14:20 +0400, Alexandre <alxgomz@gmail.com> написал:
I don't know much about blade, but have you tried other aoe targets? For instance I know ggaoed have an option to use directIO, thus disabling any caching (and decreasing performance I guess, although I never measured this precisely). This option typically ensure data constancy, which seems to be  what you're trying to achieve.

On 6 Mar 2013 02:22, "PV" <pv2pv@pochta.ru> wrote:
Hello all,
I`ve tested this software and see, that I can`t turn off write cache. "Write cache off" can be a great feature for use with DRBD or so on.
Recently I`ve tested AOE with DRBD. Everything was working fine, but when I turn off primary server and then start AOE at secondary while writing data - there was data corruption.
iSCSI target has "write cache off" options and data was written correctly.
But as for me, AOE is faster, simplier and Windows client don`t hang while switching vblade from one server to another.
May be somebody can patch sources or tell me another way to turn off write cache?
Looking at the source of vblade-20, I see that this function perform write:
 
linux.c
...
int
putsec(int fd, uchar *place, vlong lba, int nsec)
{
        return pwrite(fd, place, nsec * 512, lba * 512);
}
...
So need to sync write queue before return?
May be using function
blk_queue_flush(q, REQ_FLUSH | REQ_FUA)
?
If it will be usefull, I can give additional information about versions, testing methods and so on.
 
PV.
 
 

 
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