October 2007
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Day 2007.10.04

Correcting editing errors in AppleInsider’s ZFS article

Due to space limitations, AppleInsider’s latest ZFS article was published with several missing phrases and explanations. As a service to the community, we are happy to fill in the gaps in the story as published.

ZFS to play larger role in future versions of Mac OS X

Since Apple has stated publicly that Mac OS X 10.5 “Leopard” will include a read-only implemenation of ZFS, and since the current version of Mac OS X has no support for ZFS, this headline is unquestionably true. The rest of the article is not so lucky.

Sun Microsystems’ relatively new ZFS filesystem will see rudimentary support under the soon-to-be released Mac OS X Leopard, but will eventually play a much larger role in future versions of the Apple operating system, AppleInsider has been told.

…by Apple’s engineering management? By file system experts?

People familiar with the matter reveal that Apple on Wednesday provided developers with “ZFS on Mac OS X Preview 1.1” and associated documentation, in which the company asserted that it alone was responsible for porting the filesystem to Mac OS X.

Ah. The first paragraph should have ended with the text “…by people who leak pre-release code and know nothing about ZFS.” AppleInsider apologizes for the misunderstanding.

The Cupertino-based firm also officially confirmed to developers receiving the pre-release software that Mac OS X 10.5 Leopard — due out later this month — will officially support ZFS, albeit restricted to a read-only implementation with which no ZFS pools or filesystems can be modified.

“…as Apple stated publicly in June, as reported by our own corporate sister site, and therefore did not need confirmation, which we’re not supplying anyway since this is all third-hand rumor.”

Developers receiving the latest ZFS preview, however, are granted access to full read and write capabilities under Leopard, including the ability to create and destruct ZFS pools and filesystems.

“…where by ‘destruct,’ we mean ‘destroy,’ or would if we knew anything about ZFS. Write capabilities are no big secret, since the entire file system is open source, but it sounds a lot better if we portray it as something mystical.”

The developer release, those people familiar with the matter say, is a telltale sign that Apple plans further adoption of ZFS under Mac OS X as the operating system matures. …

“…unlike most Apple technologies, which, as far as ‘people familiar with the matter’ apparently think, are never advanced after initial release.”

… It’s further believed that ZFS is a candidate to eventually succeed HFS+ as the default operating system for Mac OS X — an unfulfilled claim already made in regard to Leopard by Sun’s chief executive Jonathan Schwartz back in June.

“This claim, by the way, is widely believed by Johnathan Schwartz, cultists who assume that Apple’s advanced file system must be bad but Sun’s must be good, and people who know so little about HFS Plus and ZFS that they can’t do more than recite Sun’s marketing propaganda. For those keeping score at home, we at AppleInsider fall into the latter group.”

Unlike Apple’s progression from HFS to HFS+, ZFS is not an incremental improvement to existing technology, but rather a fundamentally new approach to data management. …

“… or, at least, that’s what Sun’s marketing department tells us, and we’re far too ignorant to figure out that using significantly more disk space and processor time to store the same data is not ‘fundamentally new.'”

It aims to provide simple administration, transactional semantics, end-to-end data integrity, and immense scalability.

“We don’t find HFS Plus administration to be complex, and we can’t tell you what those other things mean, but they sound really cool, and therefore we want them. On the magic unlocked iPhone. For free.”

According to Sun’s description of ZFS, the filesystem offers a pooled storage model that completely eliminates the concept of volumes and the associated problems of partitions, provisioning, wasted bandwidth and stranded storage. Thousands of filesystems can draw from a common storage pool, each one consuming only as much space as it actually needs. Therefore, Sun says, the combined I/O bandwidth of all devices in the pool is available to all filesystems at all times.

“We like how this somehow implies that hard disks can suddenly read and write for multiple clients at once, but we apparently aren’t aware that this is not true, and you’re still limited to the speed of your bus (or RAID controller) and your devices. Plus, ZFS can be a lot slower because it imposes tons of overhead on the kind of tiny files that Mac OS X uses by the thousands, but maybe magic hard disks will fix that, as far as we know.”

In addition, ZFS provides a feature called “disk scrubbing,” which is similar to ECC memory scrubbing; it reads all data to detect latent errors in the file system while they’re still correctable.

“… but can only correct them if you’re using ZFS’s RAID-like capability to store duplicate copies of information, in which case a standard RAID system could fix the error too. Oops.”

“A scrub traverses the entire storage pool to read every copy of every block, validate it against its 256-bit checksum, and repair it if necessary,” the description reads. “All this happens while the storage pool is live and in use.”

“It can only correct the error if you’re using RAID and have a good copy of the bad data, but leaving that out makes you want ZFS a lot more. So does leaving out its battery-chomping, disk-eating storage hog nature that makes it fantastic for 20TB disk arrays and entirely, completely unsuitable for a Mac OS X startup disk, now or in the foreseeable future.”

A more comprehensive description of ZFS, along with several other features it offers, is available on Sun’s OpenSolaris website.

“It didn’t make us understand anything, but it repeats all these same phrases so it’ll make you think we know what we’re talking about, even though we don’t.”