Hi All,

I am designing a new server for a customer.

Looking over the differences between an "enterprise 24x7"
SATA II drive and a SAS drive, the only thing I am finding
is that SAS is better for databases, as it can do several
I/O's on a single rotation and SATA is one rotation per I/O.

Since I am not running a database, just file sharing, I do
not see the difference. I will go with the cooler, quieter,
cheaper (but not by much) "enterprise" SATA drives. Any
comment?

Also, if I am not mistaken, the way Linux works is that
the first read will be from the hard drive and consequent
reads of the same data will be from cache. Cache being
a lot faster than any hard drive. So, if I do ever get
a database and everyone is reading pretty much the same data,
SAS vs SATA means nothing as everything needed will
(eventually) be in cache anyway. Any comments?

Many thanks,
-T

Todd wrote:
> Hi All,
>
> I am designing a new server for a customer.
>
> Looking over the differences between an "enterprise 24x7"
> SATA II drive and a SAS drive, the only thing I am finding
> is that SAS is better for databases, as it can do several
> I/O's on a single rotation and SATA is one rotation per I/O.
>
> Since I am not running a database, just file sharing, I do
> not see the difference. I will go with the cooler, quieter,
> cheaper (but not by much) "enterprise" SATA drives. Any
> comment?

I run 6 10,000 rpm SCSI hard drives on my machine. They do not run hot.
They are running between 37C and 42C according to smartctl.

I do not know what temperature SAS drives run at, but I would not expect
them to run much hotter.

These drives are in the top of a full tower with 4 cooling fans.

The motherboard and all the stuff on it are in the bottom of the case that
has three intake fans and one exhaust fan, so it is running at 50C. The
processors are running at 53.5C and 57C.
>
> Also, if I am not mistaken, the way Linux works is that
> the first read will be from the hard drive and consequent
> reads of the same data will be from cache. Cache being
> a lot faster than any hard drive. So, if I do ever get
> a database and everyone is reading pretty much the same data,
> SAS vs SATA means nothing as everything needed will
> (eventually) be in cache anyway. Any comments?

If you have enough cache. This machine has 8 GBytes of RAM, and about 80% is
cache. If your database is small enough, that might be enough. I would
settle for getting the indexes into the cache.

Also, if you do any writing to the database, you will need to write to the
hard drives no later than when you do a COMMIT, and perhaps more often than
that.

The main reason I run SCSI drives is just because I want to overlap the disk
operations as much as possible, and I cannot do that as well with EIDE drives.

I assume SATA drives are a lot like ATA drives, and that SAS drives are a
lot like SCSI drives as far as their operations go. True, the
interconnections are serial instead of parallel, and a single drive may be
faster than the older ones.
>
> Many thanks,
> -T


--
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On Mon, 29 Jun 2009, Todd wrote:

> Since I am not running a database, just file sharing, I do
> not see the difference. I will go with the cooler, quieter,
> cheaper (but not by much) "enterprise" SATA drives. Any
> comment?

I have several general-purpose (NFS,SMB) file servers, some with SAS (10k)
and some with SATA, all running CentOS 5 on Dell PE2900's with hardware
RAID, all with 16GB memory. The SATA systems were purchased for cost
reasons. Had I to do it over again, and had the budget, I'd drop SATA and
go with SAS every time. The performance difference between the systems is
huge. For single-stream applications SATA is not enormously slower than
SAS, but for multiple accessors SATA is a disaster in our environment.

Steve

Steve Thompson wrote:
> On Mon, 29 Jun 2009, Todd wrote:
>
>> Since I am not running a database, just file sharing, I do
>> not see the difference. I will go with the cooler, quieter,
>> cheaper (but not by much) "enterprise" SATA drives. Any
>> comment?
>
> I have several general-purpose (NFS,SMB) file servers, some with SAS
> (10k) and some with SATA, all running CentOS 5 on Dell PE2900's with
> hardware RAID, all with 16GB memory. The SATA systems were purchased for
> cost reasons. Had I to do it over again, and had the budget, I'd drop
> SATA and go with SAS every time. The performance difference between the
> systems is huge. For single-stream applications SATA is not enormously
> slower than SAS, but for multiple accessors SATA is a disaster in our
> environment.
>
> Steve

Hi Steve,

That was exactly the feedback I was looking for. I will switch
my configuration over to SAS drives.

SAS drives have come down in price too. They are only about
$50.00 more expensive than "enterprise" level SATA drives.

Thank you!
-T