A closer look at Snow Leopard Server

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With its emphasis of iPhone advances, last week’s Worldwide Developers Conference might not have seemed to offer much in the way of Mac news—at least, not much that wasn’t covered by the conference’s non-disclosure agreement. But Apple quietly made a few Mac-centric announcements about the future of the Mac OS.

Apple confirmed the existence of the next major update to OS X, code-named Snow Leopard, as well as its accompanying OS X Server update. And while it’s been widely reported that the client version of Snow Leopard offers no new features—well, one new feature, if you count Exchange 2007 support—there’s a bit more to discuss about Snow Leopard Server.

Here’s a closer look at what Apple has revealed about the next major OS X Server update and what it means when the finished version arrives in a year or so.

Address Book Server

Address Book Server is just what it sounds like: a companion to Mac OS X Server’s e-mail and iCal servers, only centered on managing a company’s contacts. Address Book Server is based on an emerging standard, CardDAV. It sounds a lot like the standard behind iCal Server, or CalDAV, and that’s deliberate. Just as CalDAV combines standards like WebDAV and iCalendar, CardDAV combines WebDAV and vCards to create a server that allows for shared calendaring for a company.

In theory, the current Mac OS X Server already offers this, via Open Directory and LDAP. However, LDAP is a rather complicated protocol—as one WWDC attendee said, “LDAP is lightweight in the same sense that a hippo is lightweight compared to an elephant.” What’s more, in Open Directory, LDAP is used to store not only contact information, but account information, user IDs, and other IT-related information that you don’t want schussing around or out of your network. True, there are ways to prevent this, but it’s terribly easy to make a minor mistake and reveal far more than you intended. Also, if you want to tie LDAP data into a web interface, you have to do a lot of data translation. Finally, fine-grained access control for LDAP is not simple for the uninitiated.

With CardDAV, you can only expose contact information, because that’s all it understands. Since WebDAV is based on HTTP, it’s a fairly lightweight protocol that easily translates to web interfaces. And since CardDAV is based on WebDAV, it gets fine-grained access control in a fairly easy to implement manner for free. Using vCards as the data format means that using that data within web or desktop applications is a well-solved problem. Because CardDAV is not only an open standard, but lightweight and easy to implement, it is easier for vendors to implement CardDAV with existing products, in the same way that many have implemented CalDAV.

Of course, Address Book Server has only been available to developers for a few days at this point. It will be some time before we know how well this works in practice.


Throughout its history, the computer industry tends to embrace “magical thinking”, in that it seems to love imbuing the latest technology with near mystical powers. ZFS has often found itself hailed as this type of magic bullet. And while it may not be the cure-all some would like it to be, ZFS does provide an answer to a lot of real problems in an elegant fashion.

One of the problems that any administrator sees with different disk formats, such as HFS+, NTFS, UFS, and so forth, is that they simply were not designed for the massive sizes of both the disks they’re being asked to work on or the numbers and sizes of files they have to contain. That’s not to say they aren’t excellent tools, but when you start running things like HFS+, NTFS, and UFS on multi-terabyte, multi-hundred terabyte, and larger array sizes, their limitations become evident. Even with tricks like journaling, if something goes wrong, fixing it can take a long time. And the larger the numbers in the filesystem, the less of a guarantee you have that you even can repair it. Things like RAID, snapshots, and other reliability enhancements are grafted onto these filesystems, and they help. But as anyone with a kit car knows, no matter how much you graft onto a VW engine, it’s still not a jet car.

With ZFS, Sun looked far ahead and built a filesystem designed to work not where things had been, but where they were going. So instead of utilities like chkdsk and fsck, ZFS works overtime to prevent damage from happening at all. Snapshots, error correction, and redundancy are part of ZFS’s design from the start, along with support for storage pools and dynamic volume expansion. Whereas most filesystems are 64-bit filesystems, ZFS is a 128-bit filesystem, so its upper limits are, in comparison, effectively infinite. (Yes, I know that even a 128-bit filesystem will one day be too small, but not any time soon, ergo, effectively infinite.)

Using ZFS as the boot/root filesystem is still in that “so bleeding edge it will cut you” stage, according to the OpenSolaris ZFS Boot Project FAQ, and it tends to use a somewhat significant amount of CPU to do its thing. So while it’s not ideal for a consumer-level filesystem, ZFS is a fantastic filesystem for server storage needs, where file and filesystem integrity are prime uses for resources instead of something like Photoshop or World of Warcraft.

Your typical iMac user may not care about multi-exabyte volumes and support for billions of files in a directory. But for servers supporting large numbers of users and processes, these issues are moving from the “flying zeppelin city” stage into “we’ll need this in a couple years” mode, and those are the kinds of problems ZFS will solve.

Other additions

Mac OS X 10.5 moved a lot of the OS to 64-bit, and Snow Leopard finishes this. By having a 64-bit kernel, the OS can support up to 16 terabytes of RAM, larger numbers of running processes, and so on. Along with ZFS, moving the last parts of the OS to 64-bit helps future-proof Mac OS X and allow for (hopefully) bigger and better hardware to put it to work.

As for iCal Server and Mail Server, the big additions introduced in Snow Leopard Server will be push support (for iCal Server), better scalability, and an easy way to create server-side email filters/rules (for Mail Server). The end result is that no matter what device you use to manage your e-mail, they’ll all see the same thing.

Finally, Snow Leopard Server improves the Mac OS X 10.5 Server Wikis by adding multi-wiki searching. It also adds Quick Look integration for attachments, better remote access options, and a new version of Podcast Producer.

Final thoughts

Snow Leopard Server is a bit of an anomaly, in that usually, the core OS gets most of the new tricks in comparison to Server. This time, the majority of new features are server-specific new features, along with all the performance and reliability improvements Apple is making in the client version of Snow Leopard. So in a sense, this forthcoming OS X update is almost an IT-centric release. Others will disagree, but I have to say, I’m kind of happy with that.

[John C. Welch is a senior systems administrator for The Zimmerman Agency, and a long-time Mac IT pundit.]

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