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From Igor <i...@4friends.od.ua>
Subject Re: SSTable size versus read performance
Date Thu, 16 May 2013 20:27:45 GMT
just in case it will be useful to somebody - here is my checklist for 
better read performance from SSD

1. limit read-ahead to 16 or 32
2. enable 'trickle_fsync' (available starting from cassandra 1.1.x)
3. use 'deadline' io-scheduler (much more important for rotational 
drives then for SSD)
4. format data partition starting on 2048 sector boundary
5. use ext4 with noatime,nodiratime,discard mount options

On 05/16/2013 10:48 PM, Edward Capriolo wrote:
> I was going to say something similar I feel like the SSD drives read 
> much "more" then the standard drive. Read Ahead/arge sectors could and 
> probably does explain it.
>
>
> On Thu, May 16, 2013 at 3:43 PM, Bryan Talbot <btalbot@aeriagames.com 
> <mailto:btalbot@aeriagames.com>> wrote:
>
>     512 sectors for read-ahead.  Are your new fancy SSD drives using
>     large sectors?  If your read-ahead is really reading 512 x 4KB per
>     random IO, then that 2 MB per read seems like a lot of extra overhead.
>
>     -Bryan
>
>
>
>
>     On Thu, May 16, 2013 at 12:35 PM, Keith Wright
>     <kwright@nanigans.com <mailto:kwright@nanigans.com>> wrote:
>
>         We actually have it set to 512.  I have tried decreasing my
>         SSTable size to 5 MB and changing the chunk size to 8 kb
>
>         From: Igor <igor@4friends.od.ua <mailto:igor@4friends.od.ua>>
>         Reply-To: "user@cassandra.apache.org
>         <mailto:user@cassandra.apache.org>" <user@cassandra.apache.org
>         <mailto:user@cassandra.apache.org>>
>         Date: Thursday, May 16, 2013 1:55 PM
>
>         To: "user@cassandra.apache.org
>         <mailto:user@cassandra.apache.org>" <user@cassandra.apache.org
>         <mailto:user@cassandra.apache.org>>
>         Subject: Re: SSTable size versus read performance
>
>         My 5 cents: I'd check blockdev --getra for data drives - too
>         high values for readahead (default to 256 for debian) can hurt
>         read performance.
>
>


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