IDS Forum

Re: Performance issue with ZFS

Posted By: Art Kagel
Date: Monday, 26 July 2010, at 11:34 a.m.

In Response To: Re: Performance issue with ZFS (KHURRAM SHAHZAD)

Yes, sorry senior moment. UFS is simple.

The primary problem with ZFS for databases that I know of (unlike EXT4 is is
safe) is that ZFS, like most journaling filesystems, relocates disk blocks
when they are written to. That has two implications for databases that
don't affect flat files as severely: 1- since the FS block size is usually
substantial (128K or larger) and the database's block size is small (for
Informix 2K to 16K max) that means that large disk blocks will be completely
rewritten many times as data is saved and updated by the database and each
time moved to somewhere other than where it was moments ago which brings to
the second problem 2- Informix assumes the contiguous pages within a chunk
are physically contiguous, journaling filesystems break that relationship.

IDS 11.50, because non-blocking checkpoints allow us to tune the engine to
use more chunks writes which are sequential block writes, is less affected
by the first problem, but more seriously affected by the second problem than
earlier releases which had to be tuned to favor the smaller, more random,
LRU writes. That means that 11.50 will have more long transactions under
ZFS than earlier releases, but in either case the additional overhead of
rewriting and moving disk blocks repeatedly robs the system of IO bandwidth.

Simple filesystems do not experience any of these overheads. RAW is
definitely superior, and considerably faster, than COOKED devices which are
considerably faster than any filesystem, but simple filesystems are faster,
for the IO patterns of databases, than the more advanced filesystems. Note
that the main advantage of journaling filesystems is the added security of
the journal to prevent data loss in case of a system crash. Note that ALL
modern databases, and Informix is one of the most advanced in this way
alone, have their own logging systems. Informix's logical logs perform the
same function at the level of a single transaction and do it more securely
and recover much faster than any journaled filesystem since their operations
are optimized for the kinds of transactions that databases make. The
filesystem journaling is not only redundant, but will slow down recovery if
there is a crash.

Art

Art S. Kagel
Advanced DataTools (www.advancedatatools.com)
IIUG Board of Directors (art@iiug.org)

Disclaimer: Please keep in mind that my own opinions are my own opinions and
do not reflect on my employer, Advanced DataTools, the IIUG, nor any other
organization with which I am associated either explicitly, implicitly, or by
inference. Neither do those opinions reflect those of other individuals
affiliated with any entity with which I am affiliated nor those of the
entities themselves.

On Mon, Jul 26, 2010 at 10:10 AM, KHURRAM SHAHZAD <kshahzad02@i2cinc.com>wrote:

> The old SunOS filesystem? is it UFS?
>
>
>
> *******************************************************************************
> Forum Note: Use "Reply" to post a response in the discussion forum.
>
>

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Messages In This Thread

• Performance issue with ZFS
  KHURRAM SHAHZAD -- Monday, 26 July 2010, at 6:47 a.m.
  • Re: Performance issue with ZFS
    Art Kagel -- Monday, 26 July 2010, at 7:40 a.m.
    • Re: Performance issue with ZFS
      KHURRAM SHAHZAD -- Monday, 26 July 2010, at 7:56 a.m.
      • Re: Performance issue with ZFS
        Obnoxio The Clown -- Monday, 26 July 2010, at 7:59 a.m.
      • Re: Performance issue with ZFS
        KHURRAM SHAHZAD -- Monday, 26 July 2010, at 9:04 a.m.
        • RE: Performance issue with ZFS
          Wyza, Jonathon -- Monday, 26 July 2010, at 10:07 a.m.
        • RE: Performance issue with ZFS
          Paul S Card -- Monday, 26 July 2010, at 10:09 a.m.
          • Re: RE: Performance issue with ZFS
            KHURRAM SHAHZAD -- Monday, 26 July 2010, at 10:18 a.m.
            • RE: RE: Performance issue with ZFS
              Paul S Card -- Monday, 26 July 2010, at 10:31 a.m.
              • Re: RE: RE: Performance issue with ZFS
                KHURRAM SHAHZAD -- Monday, 26 July 2010, at 11:53 a.m.
                • Re: RE: RE: Performance issue with ZFS
                  Art Kagel -- Monday, 26 July 2010, at 12:01 p.m.
                  • Re: Performance issue with ZFS
                    Obnoxio The Clown -- Monday, 26 July 2010, at 12:03 p.m.
                • RE: RE: RE: Performance issue with ZFS
                  Paul S Card -- Monday, 26 July 2010, at 12:31 p.m.
                • RE: RE: RE: Performance issue with ZFS
                  Paul S Card -- Monday, 26 July 2010, at 12:45 p.m.
      • Re: Performance issue with ZFS
        Art Kagel -- Monday, 26 July 2010, at 9:29 a.m.
        • Re: Performance issue with ZFS
          KHURRAM SHAHZAD -- Monday, 26 July 2010, at 10:10 a.m.
          • Re: Performance issue with ZFS
            Art Kagel -- Monday, 26 July 2010, at 11:34 a.m.
            • Re: Performance issue with ZFS
              KHURRAM SHAHZAD -- Monday, 26 July 2010, at 12:57 p.m.
              • Re: Performance issue with ZFS
                Art Kagel -- Monday, 26 July 2010, at 3:20 p.m.

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