ATA disk performance

[hpuxsa]

We are looking at buying a new disk array and the choices are EVA3000 and Clarion CX500. Could you please recommend which would be a better option ?

Do you recommend running a disk array which would be conneted only to development systems with ATA disks on it. I have seen ATA disks being recommended for offsite backups. How would compare the performance between ATA disks and the normal disks?

[Uwe Zessin · Accepted solution]

You say you are working in development environment. Does that mean that you need flexibility in disk assignments? That is an area where the EVA really shines.

You can create virtual disks ranging from 1 GByte to 2 TByte in 1 GByte steps and you can grow them any time (provided you have free space in the disk group, of course).

I have talked to somebody from EMC a few days ago and he told me that the CX uses conventional RAID technology.

About that ATA disks... They are intended for so-called 'reference data'. That is data like pictures or scanned images that remain mostly untouched. I was in a session about ATA storage and got told that the disk drive vendors were shy to even give one (1!) year of warranty to their products.

ATA disks are mechanically not that fast like SCSI disks, but for 'reference data' they don't need to.

Honestly, I would not like to see my developers storing valuable data on that #$**%.

[Leif Halvarsson_2]

Hi,
The major drawback with the EVA3000 is the limited number of disks (max. 56). CX 500 is more scalable (120 disks).

ATA or IDE disk arrays may be a price attractive when you don't need enterprize performance. For example: workgroup fileservers, disk backup solutions, test and development enviroments. ATA and IDE disks is not as fast as SCSI ( seek time, IOPS).

I have used a such disk array (Fibrenetix ZeroD 400) for some time and never had any problem with it.

[hpuxsa]

Zesin,

Could you please explain what are the limitation on traditional RAID technology when compared to the flexibility of disk allocation we have on EVA3000

[Leif Halvarsson_2]

Hi,
Some differences:
In a EVA array you can assign any number of disks in a disk group and then configure LUNs with different RAID levels in that group (different RAID levels can be mixed on the same disks.

With a conventional RAID controller you have to assign a number of disks into a RAID set, and select a RAID level for all LUNs in that set. The number of disks in a set is limited and LUNs can't span across RAID sets.

Sure, a conventional RAID controller needs more carful planning and more "hands on" when configuring.

[Ray Ball]

I think the two major issues are performance (because random I/O on ATA will never rival what you get from FC drives, but serial I/O can rival FC drives - if configured properly)and application (e.g., reading/writing streaming video and backup-to-disk are logical applications for ATA, but a highly used transactional DB would be a poor choice).

On the CX500, with the most current O/S release (DART 13) you can use RAID-3 groups of 4+1 and 8+1 to get terrific serial I/O. But keep in mind that rebuild times on ATA RAID Groups can be VERY lengthy, e.g., >24 hours, now that you can get 320GB drives.

Do your homework so you go into this purchasing decision fully informed and with realistic expectations. You could shot yourself in the foot otherwise. Good luck.