Re: [squid-users] Re: Hypothetically comparing SATA\SAS to NAS\SAN for squid.

On 01/22/2014 03:06 PM, babajaga wrote:
>> IOs have a variable size and for writing an object to a file with the aufs
> store,
> the OS write meta data to the file system log, updates the inode table and
> writes the data to a new file.
> So for aufs for one logical 'write object to disk' there are 3 IOs.
> I do not know the internals of rock fs but most likely only does one IO for
> each 'write object to disk'. <
>
> I do not think, that this is correct. For aufs it might be 3 "logical" IOs,
> which mean,s from the standpoint of view of application (i.e.squid/aufs).
> But because LINUX does a lot of bufffering/merging, in very rare scenarios
> these 3 "logical" IOs will be real "physical"IOs (disk accesses).

The 3 mentioned I/Os are for log, inode and data. Multiple logical Log IOs can be combined into one physical IOs,
logical inode IOs can be combined into physical IOs, data IOs of different files are rarely combined.
I do not want to discuss file system IOs into too much detail here, the squid group is not meant for that.

The important thing is about understanding that aufs and rock fs are different and
cause different IO patterns.

> For rock, the one "logical"IO does not necessarily result in one "physical"
> IO either.
> So, depending upon the size of the necessary storage, the amount of RAM, and
> tweaking the LINUX-fs, the number of physical IOs is much lower compared to
> the number of "logical" IOs, squid/aufs executes.
> (ext4 for example has a lot of knobs for performance tuning)
>
>
>
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Received on Wed Jan 22 2014 - 17:21:53 MST