ZFS comes with the OS at no additional charge. It offers some of the benefits of technology that belonged in the high end and enterprise markets to low and mid range users. Sure, some of the technologies are available in other file systems for the lower end market but ZFS brings them together and gives a pretty clean interface for managing what is underneath a relatively complex system.

It’s ideal where money is tight, knowledge is limited and performance isn’t a driving force.

In particular, not only did I note ZFS’s marginally superior detection of otherwise undetectable errors (which are orders of magnitude less common than detectable but uncorrectable errors - in the absence of scrubbing the primary cause of data loss in high-density arrays when a rebuild is required), but I also mentioned that WAFL had comparable integrity-checking mechanisms (and, incidentally, it had them before ZFS did). Leaving aside the fact that IBM’s i-series (previously AS/400, nee System 38) systems have included supplementary data-integrity checksums for decades (as have high-end block-storage devices like EMC’s Symmetrix): these are also comparably capable of catching uncorrected and even undetected bit-rot on a disk, though less capable of detecting wild or lost writes.

Thus the ZFS developers reveal only their own ignorance when stating that no external storage systems provide comparable data integrity - and in general the acm article cited reads more like Sun marketing literature than like a serious journal submission (not to mention having been conducted by a Sun moderator…).

- bill

Change:
$ zpool create mypool /dev/sda1

To:
$ zpool create mypool /dev/sda

- kate

http://www.acmqueue.org/modules.php?name=Content&pa=showpage&pid=504

They say things like, a modern hard drive always devote 20% of its capacity to error correcting codes. Some of the errors cant even be detected nor corrected. And the larger the drives, more causes of silent data corruptions will occur. Unless you use ZFS of course, which fixes all these problems.

The link above is copied from this Linux user who tries out ZFS (from slashdot) for his reliable home file server:

http://breden.org.uk/2008/03/02/home-fileserver-i%e2%80%99ll-use-zfs/

1. Pooled storage while a good idea is hardly a new one, nor is ZFS’s implementation nearly as automated as it might be (e.g., RAID groups still have to be defined manually, disk by disk - just as with a conventional LVM).

2. RAID-Z might more reasonably be described as ‘brain-damaged’, given that it has dramatically *more* overhead than conventional RAID-5: every small write operation hits every disk in the stripe (rather than writes to just two of the disks after reading them - with at least one of the reads often satisfied in cache), and (even worse) every small *read* operation hits all but one of the disks in the stripe.

3. ‘Always consistent disk space’ has been available in many file systems - e.g., VxFS, XFS, JFS, NTFS, WAFL - since the early ’90s, the last of which is a copy-on-write implementation (the others use a transaction log to protect internal integrity, which has advantages in minimizing fragmentation in files which are updated at fine grain but may be read in bulk - especially since last I knew ZFS had no defragmenter).

4. Disk scrubbing has been available in Linux for years - and it’s analogous to RAM scrubbing, not to ECC (it only detects errors, allowing some other mechanism to correct them if sufficient redundancy exists to do so). ZFS’s additional internal checksums can (like similar checksums in NetApp’s WAFL) catch some errors that conventional scrubbing can’t - perhaps improving the 99.99% of otherwise undetected errors that conventional scrubbing would catch to 99.999% (yes, some people actually need this last decimal place of reassurance, but probably not very many).

5. Snapshots are relatively old hat by now (thanks to NetApp’s leading the way 15 years ago). Clones are more interesting, but arguably far less important.

6. Built-in compression has been part of NTFS since one of the early NT releases, and standard (though layered) compression on commodity platforms dates back to Microsoft DOS in the ’80s. Given storage prices these days, far fewer people bother using it than used to (not that it isn’t nice to have for special needs).

I really applaud Sun’s initiative in what has otherwise been a sadly-neglected area of corporate system development, but am less happy about the degree of hype (”ZFS - The Last Word In File Systems” being particularly notable) in which ZFS has been wrapped for public consumption. So I tend to comment upon the latter when it happens to cross my path.

One place where I disagree with this article though is how to install ZFS on FUSE. If you look at his blog site (http://zfs-on-fuse.blogspot.com/), you’ll see that he recommends running the latest code out of the mercurial trunk. That’s what I’ve been doing and I haven’t had any issues.