Message-ID: <4B89EB7C.8040606@cheapcomplexdevices.com>
Date: Sat, 27 Feb 2010 20:05:16 -0800
From: Ron Mayer <rm_pg@cheapcomplexdevices.com>
User-Agent: Thunderbird 2.0.0.23 (X11/20090817)
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To: Bruce Momjian <bruce@momjian.us>
CC: Greg Smith <greg@2ndquadrant.com>,
	Ron Mayer <rm_pg@cheapcomplexdevices.com>,
	pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: SSD + RAID
References: <201002272016.o1RKGXp26284@momjian.us>
In-Reply-To: <201002272016.o1RKGXp26284@momjian.us>
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Bruce Momjian wrote:
> Greg Smith wrote:
>> Bruce Momjian wrote:
>>> I have added documentation about the ATAPI drive flush command, and the
>>   
>> If one of us goes back into that section one day to edit again it might 
>> be worth mentioning that FLUSH CACHE EXT is the actual ATAPI-6 command 
>> that a drive needs to support properly.  I wouldn't bother with another 
>> doc edit commit just for that specific part though, pretty obscure.
> 
> That setting name was not easy to find so I added it to the
> documentation.

If we're spelling out specific IDE commands, it might be worth
noting that the corresponding SCSI command is "SYNCHRONIZE CACHE"[1].


Linux apparently sends FLUSH_CACHE commands to IDE drives in the
exact sample places it sends SYNCHRONIZE CACHE commands to SCSI
drives[2].

It seems that the same file systems, SW raid layers,
virtualization platforms, and kernels that have a problem
sending FLUSH CACHE commands to SATA drives have he same exact
same problems sending SYNCHRONIZE CACHE commands to SCSI drives.
With the exact same effect of not getting writes all the way
through disk caches.

No?


[1] http://linux.die.net/man/8/sg_sync
[2] http://hardware.slashdot.org/comments.pl?sid=149349&cid=12519114