On Fri, 3 Jan 2014 12:16:22 -0600 Dan Nelson <dnel...@allantgroup.com> wrote:
> In the last episode (Jan 03), O. Hartmann said: > > On Fri, 3 Jan 2014 14:38:03 -0000 "Steven Hartland" > > <kill...@multiplay.co.uk> wrote: > > > From: "O. Hartmann" <ohart...@zedat.fu-berlin.de> > > > > For some security reasons, I dumped via "dd" a large file onto > > > > a 3TB disk. The systems is 11.0-CURRENT #1 r259667: Fri Dec 20 > > > > 22:43:56 CET 2013 amd64. Filesystem in question is a single > > > > ZFS pool. > > > > > > > > Issuing the command > > > > > > > > "rm dumpfile.txt" > > > > > > > > and then hitting Ctrl-Z to bring the rm command into background > > > > via fg" (I use FreeBSD's csh in that console) locks up the > > > > entire command and even worse - it seems to wind up the pool in > > > > question for being exported! > > > > > > You can check that gstat -d > > > > command report 100% acticity on the drive. I exported the pool in > > question in single user mode and now try to import it back while in > > miltiuser mode. > > Did you happen to have enabled deduplication on the filesystem in > question? That's the only thing I can think of that would make file > deletions run slow. I have deleted files up to 10GB on regular > filesystems with no noticable delay at the commandline. If you have > deduplication enabled, however, each block's hash has to be looked up > in the dedupe table, and if you don't have enough RAM for it to be > loaded completely into memory, that will be very very slow :) > > There are varying recommendations on how much RAM you need for a > given pool size, since the DDT has to hold an entry for each block > written, and blocksize depends on whether you wrote your files > sequentially (128K blocks) or randomly (8k or smaller). Each DDT > entry takes 320 bytes of RAM, so a full 3TB ZFS pool would need at > minimum 320*(3TB/128K) ~= 7GB of RAM to hold the DDT, and much more > than that if your averge blocksize is less than 128K. > > So, if your system has less than 8GB of RAM in it, there's no way the > DDT will be able to stay in memory, so you're probably going to have > to do at least one disk seek (probably more, since you're writing to > the DDT as well) per block in the file you're deleting. You should > probably have 16GB or more RAM, and use an SSD as a L2ARC device as > well. > Thanks for the explanation. The box in question has 32GB RAM. I wrote a single file, 2,72 GB in size, to the pool, which I tried to "remove via rm" then. DEDUp seems to be off according to this information: [~] zfs get all BACKUP00 NAME PROPERTY VALUE SOURCE BACKUP00 type filesystem - BACKUP00 creation Fr Dez 20 23:14 2013 - BACKUP00 used 2.53T - BACKUP00 available 147G - BACKUP00 referenced 144K - BACKUP00 compressratio 1.00x - BACKUP00 mounted yes - BACKUP00 quota none default BACKUP00 reservation none default BACKUP00 recordsize 128K default BACKUP00 mountpoint /BACKUP00 default BACKUP00 sharenfs off default BACKUP00 checksum on default BACKUP00 compression off default BACKUP00 atime on default BACKUP00 devices on default BACKUP00 exec on default BACKUP00 setuid on default BACKUP00 readonly off default BACKUP00 jailed off default BACKUP00 snapdir hidden default BACKUP00 aclmode discard default BACKUP00 aclinherit restricted default BACKUP00 canmount on default BACKUP00 xattr off temporary BACKUP00 copies 1 default BACKUP00 version 5 - BACKUP00 utf8only off - BACKUP00 normalization none - BACKUP00 casesensitivity sensitive - BACKUP00 vscan off default BACKUP00 nbmand off default BACKUP00 sharesmb off default BACKUP00 refquota none default BACKUP00 refreservation none default BACKUP00 primarycache all default BACKUP00 secondarycache all default BACKUP00 usedbysnapshots 0 - BACKUP00 usedbydataset 144K - BACKUP00 usedbychildren 2.53T - BACKUP00 usedbyrefreservation 0 - BACKUP00 logbias latency default BACKUP00 dedup off default BACKUP00 mlslabel - BACKUP00 sync standard default BACKUP00 refcompressratio 1.00x - BACKUP00 written 144K - BACKUP00 logicalused 2.52T - BACKUP00 logicalreferenced 43.5K - Funny, the disk is supposed to be "empty" ... but is marked as used by 2.5 TB ...
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