Best HD Performance & Configuration in Tower Server

Question

Hi,

We currently have a single server, a PowerEdge SC440, which we initially brought to support 8 users, and at the time it needed to be as cheap as possible, and we only expected to grow to 16 users over 3 years, and just use it for file & print. The server is running Win2003 SBS, 2gb RAM, 1.8Ghz dual-core, and the hard disks are 2x 250GB drives, mirrored, partitioned into 50gb = O/S and 200gb = data.

However, since then we've grown to 40 users, and have started to use the Exchange server. We've also installed Google Desktop Search on everyone's workstations. In the past few weeks, we've noticed disk performance has started to become a real problem. Saving files can take up to 2 minutes, browsing the folders on shares can cause machines to hang etc. Looking at the performance monitor, I can see the network utilization is at only 2%, CPU never goes above 10%, but Average Disk Queue Length is between 7 & 30, and averages around 12. Looking online at performance recommendations, it shouldn't average over 5, so I think we've definitely got a bottleneck with the hard drives!

As there is no more space in the server to add additional hard drives, the only option left is to add either a new server, or network storage. This new server/NAS would just be for data, Exchange would remain on the main SBS server.

Looking at the options available, what would be the best configuration for the hard drives? I'm guessing the first thing to do, would be to separate the O/S and data onto different physical drives, so read/write operations between the 2 are not competing. So RAID1 for the O/S, but what is the best option for the data? RAID10 or RAID5? Would it be better to have 3x 146GB, SAS, 15K RPM drives in RAID5 (total usable space 292GB), or 4x 146GB, SAS, 15K RPM drives in RAID10 (total usable space 292GB). Am I right in thinking that RAID10 has better read speed than RAID5? Also, the server would probably need to be a tower, rather than rackmount, as we don't have any room left in our small rack. Do Dell do tower servers that can support 6 hard drives?

Any suggestions or ideas welcome!

Ben

pcmeiners · Answer

So RAID1 for the O/S, but what is the best option for the data? yes raid 1 for the OS, primarily for safety.

For the data.....RAID10 or RAID5? Raid 10 is overall faster than raid 5 until the raid 5 has many disks, then the raid 5 has superior reads, which compensates for the raid write penalty raid 5 has. With the proposed number of disks go with raid 10. If I were you maintain all the disks the same size among the arrays, get an extra disk, setup as a global hotspare,

"Am I right in thinking that RAID10 has better read speed than RAID5"

With the proposed number of disks, should be slightly faster, but with raid 5 you have a write penalty, which make the raid 10 faster overall...I never use a raid 5 with less then 4 disks. If you had a 5,6,7 disk raid 5, the larger r5 array would be overall faster...each disk over the minimum number of drives in an r5, increases speed, up to disk/motherboard bus saturation. Raid 10 is the better choice, overall it will be faster, as it has no parity creation, no extra space used on the disk due to parity, aside from somewhat safer then an r5 array (simplified explanation). Raid 10 has a better write speed then raid 5. Either raid type could be used, as most servers are approx 80% reads, 20% writes, again I would go raid 10.

"Do Dell do tower servers that can support 6 hard drives?" definitely

Dev Mgr · Answer

The SC440 doesn't have a lot of room for (more) harddrives, so to use more than just a raid 1, you'll want to look at a different server, and probably go with one with a PERC controller.

The T310 has 4 harddrive bays (cabled or hotswap)

The T410 has 6 harddrive bays (cabled or hotswap)

The T610 has 8 x 2.5" or 3.5" harddrive bays (hotswap)

The T710 has 8 x 3.5" harddrive bays, or 16 x 2.5" harddrive bays

I would agree with pcmeiners that raid 10 is a better choice than raid 5, but cost may play a role as raid 10 gets you less disk space (number of drives divided by 2 times the smallest drive's size (raid 5 yields "the number of drives minus 1 times the smallest drive's size)).

DELL-GaryS · Answer

The other guys are spot on with their advise, so I'll just add in my bit.

Really dedicated database servers are usually configured with seperate backplanes and controllers for the O/S and the Data. If you review the online configuration for the PE2900III you'll see an option for a set of hard drives in the 1x2 flex bay bay, and can be configured with a RAID 1 in the 1x2 flex bay and RAID 10 in the main bay, with different controllers for each array.

For performance you cannot beat going with the solid state drives (SSD) if you look at their performance they are many times faster than the 15k drives you are concidering, this effect is much larger than the performance differances between R5 and R10. (SSD not offered on the PE2900, need to go with the newer models like the PET610/PET710)

bjblackmore1 · Answer

Hi Guys,

Thanks for all your replies, they've been really helpful!

I would love to be able to afford to go for a SSD, but the level of space required (100GB mirrored) would add an extra £2,260 to the cost of a server (T610).

The T410 looks like the best option, if I can get the online configuration to work correctly, at the moment it doesn't seem to like the idea of me adding 2 SATA drives (raid1 for OS) & 4 SAS drives (raid10 for data), to my config, even though it gives the option in the raid config!

Thanks again for all the ehlp!

Ben

DELL-GaryS · Answer

Hi Ben,

If you run a transactional database like SQL or one of it's competitors, there is a transaction log that is nearly 100% sequential write or on recovery operations 100% sequential read. This log should be placed on the R1 with the O/S (partition the O/S array into two partitions one for the O/S and one for the transaction logs) This will get these writes off of the main data array (esp if it's on a R5) and with the seperate controllers it will not consume bandwidth needed on the data array.

Regards, Dell-GaryS

PowerEdge HDD/SCSI/RAID

Best HD Performance & Configuration in Tower Server

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