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From Edward Capriolo <edlinuxg...@gmail.com>
Subject Re: split large sstable
Date Mon, 21 Nov 2011 17:09:03 GMT
On Mon, Nov 21, 2011 at 11:26 AM, sridhar basam <sri@basam.org> wrote:

>
>
> On Mon, Nov 21, 2011 at 10:34 AM, Edward Capriolo <edlinuxguru@gmail.com>wrote:
>
>>
>>
>> On Mon, Nov 21, 2011 at 10:07 AM, Dan Hendry <dan.hendry.junk@gmail.com>wrote:
>>
>>> Pretty sure your argument about indirect blocks making large files
>>> inefficient only pertains to ext2/3 and not ext4. It seems ext4 replaces
>>> the
>>> 'indirect block' approach with extents
>>> (
>>> http://kernelnewbies.org/Ext4#head-7c5fd53118e8b888345b95cc11756346be4268f4
>>> , http://en.wikipedia.org/wiki/Ext4#Features).
>>>
>>> I was not aware of this difference in the file systems and it seems to
>>> be a
>>> compelling reason ext4 should be chosen (over ext3) for Cassandra - at
>>> least
>>> when using size tiered compaction.
>>>
>>>
> If you are using a Redhat distribution, at least in the 5.x series, make
> sure that you pass in a '-O extent' option when you create the filesystem.
> Otherwise extents are not enabled by default.
>
>
>> IMHO there is only one good reason left to use ext3. For a 100MB /boot
>> partition since the boot loaders have an easier time with it.
>>
>> EXT4 is better then EXT3 in every way. It is the default formatting for
>> RHEL. Do not fight the future.
>>
>>
>> http://www.edwardcapriolo.com/roller/edwardcapriolo/entry/a_great_reason_to_use
>>
>>
> I agree with ext4 being superior to ext3 but some constructive feedback
> about your graphs.
>
> You might want to add a legend or point out the before and after if you
> want to show difference between ext3 and ext4. I can kind of see that
> something might have changed on the Friday but without a legend it makes it
> hard to see the point you are trying to make.
>
>  Sridhar
>
>
To be clear the event was stop hadoop. Convert ext3 to ext4 start hadoop.
The black represents io-wait. As you can see after the conversion iowait
dropped significantly.

http://www.phoronix.com/scan.php?page=article&item=ext4_benchmarks&num=1

Ext3 was a fine file system but it was not designed for today's large
disks.

In particular, something that hurts Cassandra is that ext3's design is not
great for deleting large files. However with the write and compact model of
Cassandra you are deleting large files often.

So these facts:
1) major distributions now install ext4 by default
2) ext4 wins most/all benchmarks vs ext3
3) ext4 can handle bigger files and larger filesystems then ext3
4) large file deletion factoid
5) my graphs :)
6) You can upgrade and ext3 to an ext4 without a reformat (although it does
take an unmount and an fsck)

I can not see why anyone would run ext3 anymore.

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