Re: Converting ext3 to ext4 - results (Re: ext3 vs ext4)

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Author: Charles Jones
Date:  
To: Main PLUG discussion list
Subject: Re: Converting ext3 to ext4 - results (Re: ext3 vs ext4)
Bob Elzer wrote:
> In you timings, you say e2fsck now runs twice as fast. My impression was you
> are using this to say ext4 is twice as fast now. Having a fsck timing before
> you started would have shown us the real difference between fsck checks.
>
Yeah I had meant twice as fast as the initial painful one, but you are
right that isn't really helpful in comparing it to how long it takes on
ext3. We will have more data when I convert the other parition which I
am about to do.
> Thus I was pointing out, this would be false based on what each fsck was
> actually doing at the time.
>
> Knowing that it takes about an hour to convert 1TB of data on a 2TB drive,
> is very informative.
>
Indeed. Im curious to see how long it takes to defragment as well,
which isn't a big deal I guess since the defrag can be done on a live mount.
> Knowing, that tune2fs makes a little change and then fsck spits out a bunch
> of errors, which would scare a lot of people, is also informative. It made
> you nervous, but now the rest of us know not to panic when we see it.
>
Yeah all of those errors are "normal", as it is just complaining that
the checksums are not there yet. Can be scary if you are unaware of
that, especially since you could lose 2TB of data.
> And I presume your data is ok, or we would have heard something, so knowing
> the conversion works is also informative.
>
Yep everything was fine afterwards. I actually use encfs on top of that
partition, and it was unaffected as well as the unencrypted files and dirs.

-Charles
> Thanks
>
>
>
> ________________________________
>
> From:
> [mailto:plug-discuss-bounces@lists.plug.phoenix.az.us] On Behalf Of Charles
> Jones
> Sent: Friday, February 06, 2009 11:16 AM
> To: Main PLUG discussion list
> Subject: Re: Converting ext3 to ext4 - results (Re: ext3 vs ext4)
>
>
> Bob Elzer wrote:
>
>     This is informative, but I don't think the timing can be ruled
> accurate.

>     
>
> Accurate as compared to what? I was just showing what it did on my system so
> that people could get a *rough* idea of how long it would take to convert a
> large partition.
>
>
>     As I read your step, At first I thought tune2fs quit because it
> found
>     something wrong, and told you to run e2fsck first.

>     
>     But further reading says, tune2fs makes a change, and then has
> e2fsck do all
>     the grunt work converting.

>     
>
> Yes the first fsck after the conversion is the long slow one.
>
>
>     Your timings will be off, because the first e2fsck was doing all the
> hard
>     work, it was finding all the checksums and recalculating them for
> ext4, and
>     then writing them back to disk.

>     
>
> Timings will be off of what? I guess you mean if you have less or more data
> it could take longer or shorter to convert (more inodes to muck around
> with).
>
>
>     Thus you have all the I/O writes which adds a lot more time, then
> just
>     reads. Writing is slow compared to just reading, and it's not a big
> block of
>     writing, it lots of little

>
> Yes. My RAID is hardware RAID5. For a single disk or striped array it
> would probably go a bit faster.
>
>
>     It would have been nice to have an fsck before the tune2fs.

>     
>
> yeah I should have done that...I still have /raid1 to convert, which is
> exactly the same size. I will do an fsck on that one first.
>
> -Charles
>
>
>     
>     -----Original Message-----
>     From: 
>     [mailto:plug-discuss-bounces@lists.plug.phoenix.az.us] On Behalf Of
> Charles
>     Jones
>     Sent: Friday, February 06, 2009 8:45 AM
>     To: Main PLUG discussion list
>     Subject: Converting ext3 to ext4 - results (Re: ext3 vs ext4)

>     
>     Charles Jones wrote:

>     
>
>         I'm going to attempt a non-destructive conversion of a 2TB
> raid 
>         parition from ext3 to ext4. I will post the results :)

>         
>
>     Here's how it went. I did this on a system running Fedora Core 10:

>     
>     This is the partition I'm converting:
>     # df -h /dev/sdc1
>     Filesystem            Size  Used Avail Use% Mounted on
>     /dev/sdc1             1.8T  844G  991G  47% /raid2

>     
>     I unmounted it, and ran the command (and used the "time" command to
> record
>     how long it took):
>     # time tune2fs -O extents,uninit_bg,dir_index /dev/sdc1 tune2fs
> 1.41.3
>     (12-Oct-2008)

>     
>     Please run e2fsck on the filesystem.

>     
>     real    0m0.390s
>     user    0m0.010s
>     sys     0m0.012s

>     
>     Well that didn't take long at all.  Now for the fsck:
>     # fsck -pf /dev/sdc1
>     RAID2: Group descriptor 14903 checksum is invalid.  FIXED.
>     RAID2: Group descriptor 14904 checksum is invalid.  FIXED.
>     (a couple hundred of these quickly scrolled by) --^
>     RAID2: Adding dirhash hint to filesystem.

>     
>     While it was running, I checked process listing and saw:
>     root     12393  0.0  0.0   3984   696 pts/2    S+   05:59   0:00
> fsck 
>     -pf /dev/sdc1
>     root     12394 66.8 14.1 223272 219832 pts/2   D+   05:59   1:04 
>     fsck.ext3 -pf /dev/sdc1
>     This worreid me a bit at first, as I thought it should be running
>     /sbin/fsck.ext4 instead of fsck.ext3!

>     
>     It's done!
>     RAID2: 350165/244203520 files (0.8% non-contiguous),
> 228806800/488382016
>     blocks
>     real    61m11.019s
>     user    0m0.002s
>     sys     0m0.011s

>     
>     Now lets fsck again, to verify that fsck's under ext4 take less
> time: 
>     Before I run this second fsck I did notice that according to the
> drive
>     access lights, the raid was busy doing "something", even though the
> initial
>     fsck was complete.  What it is doing, I don't know - it's not
> defragging, as
>     there is a seperate e4defrag tool...Hmm. Oh well lets run another
> fsck and
>     see what happens:
>     # time fsck -pf /dev/sdc1
>     fsck 1.41.3 (12-Oct-2008)
>     RAID2: 350165/244203520 files (0.8% non-contiguous),
> 228806800/488382016
>     blocks
>     real    35m19.580s
>     user    1m48.430s
>     sys     0m41.541s

>     
>     So fsck is a little over twice as fast now. I notice that after this
> fsck,
>     there is no drive activity like there was the first time, so let's
> do it one
>     more time:

>     
>     fsck 1.41.3 (12-Oct-2008)
>     RAID2: 350165/244203520 files (0.8% non-contiguous),
> 228806800/488382016
>     blocks

>     
>     real    34m51.145s
>     user    1m47.481s
>     sys     0m41.174s

>     
>     About the same time, as the second run.  It looks like FC10 doesn't
> have the
>     e4defrag tool yet (I think requires new kernel).  When it is
> available I
>     will do a run of it and post the results as well.

>     
>     # mount /dev/sdc1 /raid2
>     # df -h /raid2
>     Filesystem            Size  Used Avail Use% Mounted on
>     /dev/sdc1             1.8T  844G  991G  47% /raid2

>     
>     # mount |grep raid2
>     /dev/sdc1 on /raid2 type ext4 (rw)

>     
>     -Charles

>     
>     
>     
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>
>
>
>


--
___________________________
Charles R. Jones II
IT Team Lead/Senior Systems Engineer
Cisco Learning Institute IT Dept
work: 602.343.1534 cell: 602.738.9993


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