From mboxrd@z Thu Jan 1 00:00:00 1970 MIME-Version: 1.0 In-Reply-To: <20120114233209.15BD4B85A@mail.bitblocks.com> References: <20120113113026.GA419@polynum.com> <20120114003032.1C08F1CC8F@mail.bitblocks.com> <201201140201.51504.dexen.devries@gmail.com> <2ca6969da468ef7d305866d2c3c484f4@chula.quanstro.net> <3a789b771cbf86e9a6e7ddfff2b95bb4@chula.quanstro.net> <20120114233209.15BD4B85A@mail.bitblocks.com> From: =?UTF-8?B?QXJhbSBIxIN2xINybmVhbnU=?= Date: Sun, 15 Jan 2012 00:45:39 +0100 Message-ID: To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [9fans] fossil pb: FOUND! Topicbox-Message-UUID: 5c72ca4a-ead7-11e9-9d60-3106f5b1d025 >> > How come? With venti, the address is the SHA-1 hash, with ZFS, you get >> > to chose the hash, but it can still be a hash. >> >> because in zfs the hash is not used as an address (lba). > > True. As I said, neither in Venti. The hash is translated to a lba by the index, a table that can be recreated from the data if it's missing or if it's corrupt. ZFS also uses an index table called DDT. It also has the same properties as Venti's index, it can be created by reading the data. > Intel 320 300GB SSD numbers (for example): > seq read: =C2=A0270MBps > rnd read: =C2=A039.5Kiops =3D=3D 158Mbps @ 4KB > seq write: 205MBps > rnd write: 23.0Kiops =3D=3D 92MBps =C2=A0@ 4KB Those are just random I/O stats, you are not interpreting them to see what the penalty would be for some chosen fragmentation/block size. I'm writing that interpretation tomorrow. > IIRC ZFS picks a much > larger block size so it suffers less here. ZFS will try to use big blocks if it can, maximum 128kB right now, but I don't see how this is relevant if you read random 4K logical blocks. Please notice that both Venti and ZFS will write a big file sequentially on the disk, that's (partially) what the index table/DDT is for. In this case, the hash of sequential blocks within a file will simply map (via the index) to sequential disk addresses. --=20 Aram H=C4=83v=C4=83rneanu