Date: Fri, 29 Apr 2016 10:03:47 -0500 From: "Eric A. Borisch" <eborisch@gmail.com> To: Ronald Klop <ronald-lists@klop.ws> Cc: "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org>, Karl Denninger <karl@denninger.net> Subject: Re: How to speed up slow zpool scrub? Message-ID: <CAASnNnqJBCVq6gZ00%2BJNFZKHen_tJYBNz-OePPkEVnOCTtf4Cg@mail.gmail.com> In-Reply-To: <op.ygoqhgabkndu52@ronaldradial.radialsg.local> References: <381846248.2672053.1461695277122.JavaMail.yahoo.ref@mail.yahoo.com> <381846248.2672053.1461695277122.JavaMail.yahoo@mail.yahoo.com> <1461736217.1121.17.camel@michaeleichorn.com> <alpine.GSO.2.20.1604290821210.23612@freddy.simplesystems.org> <08d59afe-c835-fa8d-0e52-78afcb1cc030@denninger.net> <op.ygoqhgabkndu52@ronaldradial.radialsg.local>
next in thread | previous in thread | raw e-mail | index | archive | help
On Fri, Apr 29, 2016 at 9:28 AM, Ronald Klop <ronald-lists@klop.ws> wrote: > On Fri, 29 Apr 2016 15:47:22 +0200, Karl Denninger <karl@denninger.net> >> ZFS makes the *assumption*, fair or not, that everything in its >> RAM-based caches is correct. If that assumption is violated you will >> eventually be a very sad Panda. Use ECC memory or don't use ZFS. >> > > Just like UFS makes an assumption about correct memory and correct disks? > > ECC helps ZFS as much as ECC helps UFS. > And without ECC ZFS provides more failsafes than UFS. But nothing is > perfect. > You guys make it sound like ZFS has no added benefits if you don't use ECC, > which is not true. > > UFS < ZFS < ZFS+ECC > And UFS+ECC is somewhere in between probably. > As long as people understand the risks/benefits things are ok. I a key distinction is that UFS has fsck for attempting to repair inconsistencies on the drive, where ZFS does not have a similar tool, because "[t]he only way for inconsistent data to exist on disk in a ZFS configuration is through hardware failure [...] or when a bug exists in the ZFS software." [1] So if ZFS fails, it is more likely to fail hard; enter the ECC (avoid hardware failure) "requirement". I personally have one system running without ECC, but it is a tiny system at home that serves as the firewall the cable modem runs into. It is backed up and stores nothing of real value on the media, but I love having ZFS on it because I can do things like beadm for upgrades, or diffs of /etc files with previous (automated) snapshots. (It's also running with less than 4G of RAM, tsk-tsk...) If you are storing data you care about* on a ZFS system without ECC, you are doing it wrong. If that system *is* the backup, you are in a gray area depending on your risk profile. (Is it OK if the backups fail, because I still have the source and am willing to risk having only one copy while I rebuild the backup?) So I'd temper Karl's statement to "Use ECC memory -- or really understand the risks -- or don't use ZFS." - Eric [1] http://docs.oracle.com/cd/E19253-01/819-5461/6n7ht6r6p/index.html * can't afford to lose / can't recreate
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAASnNnqJBCVq6gZ00%2BJNFZKHen_tJYBNz-OePPkEVnOCTtf4Cg>