We've got a shared cPanel server which is showing high loads. I think its high I/O usage due to using SATAII hard drives.

What do people think about switching to SAS drives? Are they really that much faster?

From my experience I'd say yes. You could go one step futhure and go SSD.

Cost a bit more but EVEN FASTER.

15,000rpm SAS drives are fantastic, the down side to SAS is the storage size I believe the largest drive you can get which is 15,krpm is 400gb drives. The 300gb drives are well priced, but you currently pay a premium for 400gb drives. 500gb drives are still 7200rpm, and are around the same price as 300gb 15k.

But if you were going to go with SAS technology I would recommend the faster drive for sure, combined with a premium hardware raid controller the performance will be far greater than any SATA platform.

The other option you could consider would be fiber channel SAN with SAS drives which would allow you to deploy a fast IO solution for more than 1 server, really depends on your budget.

Regards James

Definitely 15k SAS will make a huge difference, especially when you mix it with RAID 10 - the performance blows SATA out of the water. We have been using this on our shared/reseller hosting servers for a while now and it performs very well.

The other option if you are on a budget is to use SATA and RAID 10, you will get a significant performance increase by doing this.

Regards,
Aaron

Knowing very little about Solid-state drives (that's what your referring to yes), don't they have a high failure rate? Or am I confused..

EDIT: Yes, I might be. Just read Wikipedia, interesting

That's good to know. I will have to look into it more

Ok, talking about SANs this is an area I don't know much about it... If you grab yourself a fiber channel SAN hock it up to a few of your servers which have the required cards, than the servers are running completely off the SAN and not the internal drives? If that's the case what sort of options are available to backup the entire first SAN to a second SAN for fail over if the primary SAN dies?

you wouldnt be looking at any of the drives on offer from retail stores though.

there are many (very expensive) SSD options out there that will whip the pants of any regular drive

You would preferably get a SAN with replication, although costly it would mean you have a complete replicated copy that you can fail over to if the primary SAN fails.

Currently I believe the largest 15k SAS drive you can purchase is 450GB.

Spirit, 15K SAS is how I can almost get VPS performances from a shared hosting account. That and the 2XQuad cores and 32GB RAM.

Spirit

We run Dell 2950's with 6 x 300GB 15k SAS drives (RAID 10) with 2 x Quad core Xeons and 32 GB RAM for our Hyper-V servers. They fly along even with 10 - 15 VM's on them.

What are the differences in reading and writing speed between no RAID, RAID 1 and RAID 10?

No RAID - 1 x read, 1 x write
RAID 1 - 2 x read, 1 x write
RAID 10 (assuming 4 drives) - 2 x read, 2 x write

This is a very basic way of looking at it. RAID 10 tends to be the fastest RAID level, but you get the least amount of storage from it.

The other thing that you should do in a case like this is to work out why the load is so high. Sometimes you can get huge bang for buck if you know what to look for; other times it can be hard to get a clear picture of the cause.

Backups are a big cause of load issues; in particular, running low on memory can balloon out load and backup times by a factor of 10 or more. Running cPanel backups during the day has a huge performance hit on response times. Rsync (or rsync-based) is a lot faster if you don't need the cPanel tarballs (or don't need them as often).

Adding memory can also help with other apps; check out vmstat/iostat to see whether there's any appreciable page fault count. (if so, you'll get a big improve from adding memory)

With some apps (eg vbulletin and co) you can get a very decent improvement by tuning mysql.

Other times a user has a very badly written app which is loading the system down.

Just a few things that have helped us in the past, hope they help...

Hmm, SAN discussion.. Yum.

Fibre channel SAN's typically ship with 2 fibre channel uplink ports (you can get some which have more). There's a few ways about integrating with your new found space & speed freedom.

In the situation where you don't buy a set of switches but you do get a set of redundant SANs you generally look at getting 2 servers in failover and direct attaching things in there then sharing the space as required from those host nodes. There's a number of distributions specifically for this but for performance I've always leaned towards Solaris. Nexenta do a Solaris derivation specifically targeted at this market and they allow you to do nfs/smb/iscsi from there. When it comes to CPanel I guess you'd go the iscsi option here and either:

a) Get a iscsi initiator card in there and initiate to your storage pair.
b) Put a bootstrap startup on the hardware itself which then does an iscsi initiation and starts your real OS.

Guess I should also state that iscsi support from Solaris & Linux has shown to be far more stable then iscsi support direct from the storage kit itself. That's mainly cause the storage kit usually has a crappy CPU and the 'i' part of iscsi makes it relatively costly.

Now, the other method (the 'Enterprise' way) is if you DO get a pair of fibre channel switches. These cost around 10K each which relative to your SAN purchase isn't THAT much. You setup your SAN's so that their connections are redundantly split across your two FC switches (or 'Fabrics' as the storage people like to say). Now you've got 2 SAN's connected via diverse paths to two switches.

From there you take your actual hardware and install a dual port FC card (~$700 each) in each host. You set that up to terminate one to each switch (diverse paths to both SAN's via both fabrics).

For both the iscsi and FC option basically any decent card will offer a BIOS booting option. That's where your hard drives onbox become irrelevent (except maybe for swap) and the BIOS treats the SAN/FC volumes like a normal hard drive.

Replication wise, as usual, you have the costly and cheap option. The costly option is to get SAN's with replication capabilities out of the box. They take care of each other and you never have to think about it again (hopefully). Vendors used to charge a lot for this but the new series stuff (Hitachi & Equalogic for instance) have this shipping as standard. If you're going down this path you want to look for a SAN which has the capability to make 'virtual fabrics' seamlessly migrating between the two on failure. Otherwise your boxes are going to need a reboot or reconfiguration if your backend fails.

The cheaper option is to export two independent LUN's (1 from each SAN) then use whatever replication you want on box. On Linux this is software raid or mirrored LVM, on Solaris this is ZFS (and it's awesome ). Then if you have a SAN failure the idea is that all your boxes will register a 'dead disk' and recovering involves getting the SAN back to normal and resyncing from the good disk.

Hopefully that answers a few of your questions. There's some more tidbits in a Cluster 101 doc I did here: Seekbrain.com Cluster 101

Stu

Guess it's worth noting that RAID5 on any recent FC array will suffice for most applications.

Just cause 1 raid method is faster than another pales in significance to backend architectural layouts.

Stu