On Tue, Sep 17, 2013 at 2:20 PM, Grant <emailgr...@gmail.com> wrote: > I'm convinced I need 3-disk RAID1 so I can lose 2 drives and keep > running. I'd also like to stripe for performance, resulting in > RAID10. It sounds like most hardware controllers do not support > 6-disk RAID10 so ZFS looks very interesting. > > Can I operate ZFS RAID without a hardware RAID controller? >
Yes. In fact, that's ZFS' preferred mode of operation (i.e., it handles all redundancy by itself). > From a RAID perspective only, is ZFS a better choice than conventional > software RAID? > Yes. ZFS checksummed all blocks during writes, and verifies those checksums during read. It is possible to have 2 bits flipped at the same time among 2 hard disks. In such case, the RAID controller will never see the bitflips. But ZFS will see it. > ZFS seems to have many excellent features and I'd like to ease into > them slowly (like an old man into a nice warm bath). Does ZFS allow > you to set up additional features later (e.g. snapshots, encryption, > deduplication, compression) or is some forethought required when first > making the filesystem? > Snapshots is built-in from the beginning. All you have to do is create one when you want it. Deduplication can be turned on and off at will -- but be warned: You need HUGE amount of RAM. Compression can be turned on and off at will. Previously-compressed data won't become uncompressed unless you modify them. > It looks like there are comprehensive ZFS Gentoo docs > (http://wiki.gentoo.org/wiki/ZFS) but can anyone tell me from the real > world about how much extra difficulty/complexity is added to > installation and ongoing administration when choosing ZFS over ext4? > Very very minimal. So minimal, in fact, that if you don't plan to use ZFS as a root filesystem, it's laughably simple. You don't even have to edit /etc/fstab > Performance doesn't seem to be one of ZFS's strong points. Is it > considered suitable for a high-performance server? > > http://www.phoronix.com/scan.php?page=news_item&px=MTM1NTA > Several points: 1. The added steps of checksumming (and verifying the checksums) *will* give a performance penalty. 2. When comparing performance of 1 (one) drive, of course ZFS will lose. But when you build a ZFS pool out of 3 pairs of mirrored drives, throughput will increase significantly as ZFS has the ability to do 'load-balancing' among mirror-pairs (or, in ZFS parlance, "mirrored vdevs") Go directly to this post: http://phoronix.com/forums/showthread.php?79922-Benchmarks-Of-The-New-ZFS-On-Linux-EXT4-Wins&p=326838#post326838 Notice how ZFS won against ext4 in 8 scenarios out of 9. (The only scenario where ZFS lost is in the single-client RAID-1 scenario) > Besides performance, are there any drawbacks to ZFS compared to ext4? > 1. You need a huge amount of RAM to let ZFS do its magic. But RAM is cheap nowadays. Data... possibly priceless. 2. Be careful when using ZFS on a server on which processes rapidly spawn and terminate. ZFS doesn't like memory fragmentation. For point #2, I can give you a real-life example: My mail server, for some reasons, choke if too many TLS errors happen. So, I placed "Perdition" in to capture all POP3 connections and 'un-TLS' them. Perdition spawns a new process for *every* connection. My mail server has 2000 users, I regularly see more than 100 Perdition child processes. Many very ephemeral (i.e., existing for less than 5 seconds). The RAM is undoubtedly *extremely* fragmented. ZFS cries murder when it cannot allocate a contiguous SLAB of memory to increase its ARC Cache. OTOH, on another very busy server (mail archiving server using MailArchiva, handling 2000+ emails per hour), ZFS run flawlessly. No incident _at_all_. Undoubtedly because MailArchiva use one single huge process (Java-based) to handle all transactions, so no RAM fragmentation here. Rgds, -- FdS Pandu E Poluan ~ IT Optimizer ~ • LOPSA Member #15248 • Blog : http://pepoluan.tumblr.com • Linked-In : http://id.linkedin.com/in/pepoluan
