Узнайте размер диска индекса :
SELECT
OBJECT_NAME(I.OBJECT_ID) AS TableName,
I.name AS IndexName,
8 * SUM(AU.used_pages) AS 'Index size (KB)',
CAST(8 * SUM(AU.used_pages) / 1024.0 AS DECIMAL(18,2)) AS 'Index size (MB)'
FROM
sys.indexes I
JOIN sys.partitions P ON P.OBJECT_ID = I.OBJECT_ID AND P.index_id = I.index_id
JOIN sys.allocation_units AU ON AU.container_id = P.partition_id
WHERE
OBJECT_NAME(I.OBJECT_ID) = '<TableName>'
GROUP BY
I.OBJECT_ID,
I.name
ORDER BY
TableName