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identity=mailfrom; envelope-from="davide+p9@cs.cmu.edu"; helo=relay-05.andrew.cmu.edu; client-ip=128.2.157.12 Received: from relay-05.andrew.cmu.edu (RELAY-05.ANDREW.CMU.EDU [128.2.157.12]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by tb-mx1.topicbox.com (Postfix) with ESMTPS for <9fans@9fans.net>; Tue, 28 May 2024 22:22:27 -0400 (EDT) (envelope-from davide+p9@cs.cmu.edu) Received: from lunacy.ugrad.cs.cmu.edu (lunacy.ugrad.cs.cmu.edu [128.2.209.4]) by relay-05.andrew.cmu.edu (Postfix) with ESMTP id 595344001D6 for <9fans@9fans.net>; Tue, 28 May 2024 22:22:27 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.11.0 relay-05.andrew.cmu.edu 595344001D6 From: Dave Eckhardt To: 9fans <9fans@9fans.net> Subject: Re: [9fans] Throwing in the Towel In-reply-to: <17169248040.5f383EFCe.47999@composer.9fans.topicbox.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-ID: <8168.1716949347.1@lunacy.ugrad.cs.cmu.edu> Date: Tue, 28 May 2024 22:22:27 -0400 Message-ID: <8169.1716949347@lunacy.ugrad.cs.cmu.edu> Topicbox-Policy-Reasoning: allow: sender is a member Topicbox-Message-UUID: 4e60d0ce-1d62-11ef-94ae-b8e4cdcdbefa Archived-At: =?UTF-8?B?PGh0dHBzOi8vOWZhbnMudG9waWNib3guY29tL2dyb3Vwcy85?= =?UTF-8?B?ZmFucy9UMmNhNjc0ODZjN2ExM2E3Ny1NZmFmZTNiMGE3NGY3NWNkMjY2ZWIw?= =?UTF-8?B?YTczPg==?= List-Help: List-Id: "9fans" <9fans.9fans.net> List-Post: List-Software: Topicbox v0 List-Subscribe: Precedence: list Reply-To: 9fans <9fans@9fans.net> Content-Transfer-Encoding: quoted-printable List-Unsubscribe: , Topicbox-Delivery-ID: 2:9fans:437d30aa-c441-11e9-8a57-d036212d11b0:522be890-2105-11eb-b15e-8d699134e1fa:Mfafe3b0a74f75cd266eb0a73:1:JnTiaX_Tt25EzbxYzs_y1hx1FJ3cdGJIHr7ea1hVu3M > For the napkin calculation: On disk, the IEntry is 38Bytes. Alas, > writes occur always in (the ssd internal) blocksize. So, essentially > (assuming 4096 byte blocksize, which is quite optimistic), we have > a write efficiency of less than 1 percent. While I see how such a model can predict disaster, I don't think that model matches how FTLs work, because it can't. Many file systems (FAT, ext2/3/4) write the same logical block over and over and over and over and over. I think the default interval for ext4 to synch the superblock and the journal is five seconds, which if true is more than 15,000 times every *day* for a busy file system (and I think lots of Linux systems are busy in that sense). > A good firmware in the ssd could avoid needing a new block for the > write, if all bits are changed in teh same direction by the new > data. Again, I believe this model predicts that no regular Linux file system can be used on any SSD, thus I believe this model is not accurate. To quote Wikipedia: https://en.wikipedia.org/wiki/Flash_memory_controller > The mapping units of an FTL can differ so that LBAs are mapped > block-, page- or even sub-page-based. Depending on the usage > pattern, a finer mapping granularity can significantly reduce > the flash wear out and maximize the endurance of a flash based > storage media. Also, I feel as if this point is several assumption layers deep. I think one user reported an unknown number of failures in two sets of SSDs of unknown brand and model. I don't think we know that it was venti SSDs that went bad as opposed to fossil SSDs, let alone knowing it was index SSDs for venti. > It seems, venti in its current form is a ssd killer, if they > are used for the isects. I don't think this claim is yet supported well. Dave Eckhardt ------------------------------------------ 9fans: 9fans Permalink: https://9fans.topicbox.com/groups/9fans/T2ca67486c7a13a77-Mfafe3= b0a74f75cd266eb0a73 Delivery options: https://9fans.topicbox.com/groups/9fans/subscription