DLSLUG notes, 5-Apr-2007: Todd Underwood discusses ZFS

Fifteen attendees made it to the April meeting of the Dartmouth Lake
Sunapee Linux User Group
, held as usual in Carson Hall at the Dartmouth College campus on the first Thursday of the month.

Todd Underwood, Vice President, Operations and Professional Services at Renesys presented “ZFS: The Last Word in File Systems.” Renesys is in the business of collecting, analyzing and archiving data about what’s happening on the internet and, not surprisingly, that’s a lot of data and growing geometrically. One of Todd’s projects is to provide fast and reliable storage for the hundreds of gigabytes per day acquired and the tens of terabytes of data stored. He presented a survey of what’s out there, what his needs were, and how he reluctantly narrowed the search down to SUN Solaris and ZFS. While he had nothing but praise for ZFS, he expressed some reservations about SUN. Strong reservations.

Todd dug into the ZFS architecture. ZFS is truly amazing: disk contents are always coherent, with writes all checksummed, writes as atomic transactions, with “fancy FS internals” like IO scheduling, dynamic block sizes and prefetch queues, huge limits (128-bit data). ZFS flattens the Linux file system model of multiple layers into a single monolith, and eliminates entire classes of problems introduced by the multiple layer architecture. There is no fsck. Devices are accumulated into pools. File systems are assigned to pools. Storage addition and maintenance is fairly trivial. ZFS performance is remarkable, at disk speed (with compression, sometimes in excess of disk speed).

Todd presented the rough outlines of his storage system: $17k worth of hardware from SUN and Dell yields 7.5 terabytes of storage with nearly a gigabyte per second throughput. Todd’s disk storage challenge is solved, as the company’s demand can’t match the throughput capacity of his system, for now, and the system can be expanded with additional external storage.

As for the porting of ZFS onto other architectures, Todd expressed the opinion that running on Solaris or OpenSolaris is likely the best current solutions. Porting onto BSD is underway but not yet ready. He had heard that ZFS was ported to OS X but could not confirm (Googling ZFS OSX yields interesting results).

Todd promises to send along slides from his presentation; I’ll try to post links to them to the website.

After the main presentation, there was a good session of questions and answers. I asked a question on replication of Postgres and Todd recommended the Sequoia product.

Thanks to Todd for his thorough presentation, to Bill McGonigle for organizing the meeting, to Bill Sconce for sharing his notes with me for this post, and to all for attending and participating. Next meeting, still tentative, will be on writing a FireFox extension by Roger Trussell.

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