From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail2.shareable.org ([80.68.89.115]) by bombadil.infradead.org with esmtps (Exim 4.68 #1 (Red Hat Linux)) id 1K39D7-0001I1-8B for linux-mtd@lists.infradead.org; Mon, 02 Jun 2008 12:32:25 +0000 Date: Mon, 2 Jun 2008 13:32:18 +0100 From: Jamie Lokier To: =?iso-8859-1?Q?J=F6rn?= Engel Subject: Re: big flash disks? Message-ID: <20080602123217.GA2679@shareable.org> References: <20080601184239.GA11135@shareable.org> <1212386359.31023.154.camel@sauron> <20080602082346.GB20259@logfs.org> <20080602104330.GD31032@shareable.org> <20080602115538.GC21359@logfs.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20080602115538.GC21359@logfs.org> Cc: linux-mtd@lists.infradead.org List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Jörn Engel wrote: > Flash allows one to do partial writes to blocks. SSDs generally don't. > Logfs currently does partial writes for atomic transactions, to make > creat(), unlink(), rename() and friends behave well. Depending on your > SSD a simple creat() can blow up to writing several megabytes on the > actual medium. It's a good argument for delaying writes, and committing only the minimum necessary on fsync/fdatasync/sync_file_range. According to the slashdot comment which started this thread :-) they do 4k log writes to large SSDs - and then report a very high write IOP rate for database applications. It's the high write rate which is their selling point: price per GB is ridiculous. So I'm inclined to believe they do actually get the claimed write rate under some circumstances. If they can do 4k writes, and you cannot, it sounds like the SSDs you have used are very different to the SSDs they have used. Is that right? If so, we need to keep an open mind about the different kinds of SSD that are becoming available under that name. -- Jamie