According to research by mainframe user group Xephon Plc, the battle for mainframe disk storage is still being fought between IBM Corp and EMC Corp. In a survey of 150 mainframe sites, IBM was on top in terms of the total number of units installed with 187 arrays – 47% of the total sample – and the most widely installed, being present in 21% of sites, compared with 33% for EMC in terms of units and 17% in sites. In storage capacity installed, however, the positions were reversed. EMC drives represented 42% of the storage installed with 20,078Gb, while IBM had 39% with 18,580Gb. There was also neck and neck competition at the product level. While IBM’s Ramac2 line has the largest market share in terms of units installed, with 115 units or 29% of total, EMC’s Symmetrix 5500 was the largest in terms of capacity installed, with 31% or 14,600Gb. The other two significant vendors, Storage Technology Corp and Hitachi Data Systems Inc, shared 20% of the units installed and 18% of the installed capacity.
RAID capacity is growing
The total installed RAID redundant array of independent disk capacity of the sites surveyed has grown fairly consistently over the last three years, by around 1,000Gb to 2,000Gb per month. There were only exceptional peaks: in April 1994 and October 1995. The first peak, which saw almost 5,000Gb of storage bought in a single month, coincides with the launch of EMC’s Symmetrix 5500, according to Xephon. The second peak, where more than 9,000Gb was bought, coincides with the launch of Ramac2. In terms of reliability, performance, vendor support and value for money, all vendors and products did well. The average satisfaction rating for all vendors and products was 4.34 – where 1 denotes ‘poor’, 2 ‘mediocre’, 3 ‘satisfactory’, 4 ‘good’ and 5 ‘excellent’ – and none of the nine products fell below 4 in any of four disciplines. EMC’s Symmetrix 5200 had the highest overall rating with 4.6, while the Model 5500 had the lowest with 4.25 and overall EMC scored the best with an average of 4.46, compared with Hitachi on 4.32, IBM on 4.29 and StorageTek on 4.28. IBM’s Ramac and Ramac2 scored 4.28 and 4.29, respectively. Ramac earned the highest individual score for vendor support but the lowest for both performance and value for money. At the sites surveyed, 51% of the devices have failed at some point. EMC seems to be the worst culprit, according to Xephon. Some 61% of all EMC drives were reported as having failed, with more than three quarters of Symmetrix 5500s having suffered a failure, compared with 35% for IBM. There is a danger, however, in drawing too many conclusions from the survey results. Older devices, such as the Symmetrix 5500, are more likely to suffer wear and tear and are much more likely to have failed since they have been in use longer. On an annual basis, the Model 5500 is likely to fail about one and a half times per unit per year. All the other arrays in the survey failed less than once per unit per year – the lowest number of failures coming from the Ramac drives, which experience just over more than one failure per three units per year.
